LPI-Learning-Material-102-500-en-2.pdf

LPIC-1 (102) (Version 5.0) | 107.1 Manage user and group accounts and related system files ◦ What is the minimum password lifetime for catherine? And what is the maximum password lifetime? ◦ What is the password inactivity period for kevin? 2. By convention, which IDs are assigned to system accounts and which to ordinary users? 3. How do you find out if a user account, which was previously able to access the system, is now locked? Assume your system uses shadow passwords. Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 191 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks Explorational Exercises 1. Create a user account named christian using the useradd -m command and identify its User ID (UID), Group ID (GID) and shell. 2. Identify the name of the primary group of christian. What can you deduce? 3. Using the getent command, review password aging information for the christian user account. 4. Add the editor group to the secondary groups of christian. Assume that this group already contains emma, dave and frank as ordinary members. How can you verify that there are no administrators for this group? 5. Run the ls -l /etc/passwd /etc/group /etc/shadow /etc/gshadow command and describe the output that it gives you in terms of file permissions. Which of these four files are shadowed for security reasons? Assume your system uses shadow passwords. 192 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.1 Manage user and group accounts and related system files Summary In this lesson you learned: The location of files that store information about users and groups. Manage user and group information stored in password and group databases. Retrieve information from password and group databases. The following files and commands were discussed in this lesson: /etc/passwd The file containing basic information about users. /etc/group The file containing basic information about groups. /etc/shadow The file containing encrypted user passwords. /etc/gshadow The file containing encrypted group passwords. getent Filter the password and group databases. Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 193 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks Answers to Guided Exercises 1. Observe the following output and answer the following questions: # cat /etc/passwd | grep '$root\|mail\|catherine\|kevin$' root:x:0:0:root:/root:/bin/bash mail:x:8:8:mail:/var/spool/mail:/sbin/nologin catherine:x:1030:1025:User Chaterine:/home/catherine:/bin/bash kevin:x:1040:1015:User Kevin:/home/kevin:/bin/bash # cat /etc/group | grep '$root\|mail\|db-admin\|app-developer$' root:x:0: mail:x:8: db-admin:x:1015:emma,grace app-developer:x:1016:catherine,dave,christian # cat /etc/shadow | grep '$root\|mail\|catherine\|kevin$' root:$6$1u36Ipok$ljt8ooPMLewAhkQPf.lYgGopAB.jClTO6ljsdczxvkLPkpi/amgp.zyfAN680zrLLp2avvpd KA0llpssdfcPppOp:18015:0:99999:7::: mail:*:18015:0:99999:7::: catherine:$6$ABCD25jlld14hpPthEFGnnssEWw1234yioMpliABCdef1f3478kAfhhAfgbAMjY1/BAeeAsl/FeE dddKd12345g6kPACcik:18015:20:90:5::: kevin:$6$DEFGabc123WrLp223fsvp0ddx3dbA7pPPc4LMaa123u6Lp02Lpvm123456pyphhh5ps012vbArL245.P R1345kkA3Gas12P:18015:0:60:7:2:: # cat /etc/gshadow | grep '$root\|mail\|db-admin\|app-developer$' root:*:: mail:*:: db-admin:!:emma:emma,grace app-developer:!::catherine,dave,christian ◦ What is the User ID (UID) and the Group ID (GID) of root and catherine? The UID and GID of root are 0 and 0, while the UID and GID of catherine are 1030 and 1025. ◦ What is the name of the primary group of kevin? Are there other members in this group? The group name is db-admin. Also emma and grace are in this group. ◦ Which shell is set for mail? What does it mean? mail is a system user account and its shell is /sbin/nologin. In fact, system user accounts such as mail, ftp, news and daemon are used to perform administrative tasks and therefore normal login should be prevented for these accounts. This is why the shell is usually set to 194 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.1 Manage user and group accounts and related system files /sbin/nologin or /bin/false. ◦ What are the members of the app-developer group? Which of these are group administrators and which are ordinary members? The members are catherine, dave and christian and they are all ordinary members. ◦ What is the minimum password lifetime for catherine? And what is the maximum password lifetime? The minimum password lifetime is 20 days, while the maximum password lifetime is 90 days. ◦ What is the password inactivity period for kevin? The password inactivity period is 2 days. During this period kevin should update the password, otherwise the account will be disabled. 2. By convention, which IDs are assigned to system accounts and which to ordinary users? System accounts usually have UIDs less than 100 or between 500 and 1000, while ordinary users have UIDs starting at 1000 although some legacy systems may start numbering at 500. The root user has UID 0. Remember that the UID_MIN and UID_MAX values in /etc/login.defs define the range of UIDs used for the creation of ordinary users. From the standpoint of LPI Linux Essentials and LPIC-1, system accounts have UIDs less than 1000 and ordinary users have UIDs greater than 1000. 3. How do you find out if a user account, which was previously able to access the system, is now locked? Assume your system uses shadow passwords. When shadow passwords are used, the second field in /etc/passwd contains the x character for each user account, because the encrypted user passwords are stored in /etc/shadow. In particular, the encrypted password of a user account is stored in the second field of this file and, if it starts with an exclamation mark, the account is locked. Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 195 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks Answers to Explorational Exercises 1. Create a user account named christian using the useradd -m command and identify its User ID (UID), Group ID (GID) and shell. # useradd -m christian # cat /etc/passwd | grep christian christian:x:1050:1060::/home/christian:/bin/bash The UID and GID of christian are 1050 and 1060 respectively (the third and fourth fields in /etc/passwd). /bin/bash is the shell set for this user account (the seventh field in /etc/passwd). 2. Identify the name of the primary group of christian. What can you deduce? # cat /etc/group | grep 1060 christian:x:1060: The name of the primary group of christian is christian (the first field in /etc/group). Therefore, USERGROUPS_ENAB in /etc/login.defs is set to yes so that useradd creates by default a group with the same name of the user account. 3. Using the getent command, review password aging information for the christian user account. # getent shadow christian christian:!:18015:0:99999:7::: The christian user account does not have the password set and is now locked (the second field in /etc/shadow contains an exclamation mark). There is no minimum and maximum password age for this user account (the fourth and fifth fields in /etc/shadow are set to 0 and 99999 days), while the password warning period is set to 7 days (the sixth field in /etc/shadow). Finally, there is no inactivity period (the seventh field in /etc/shadow) and the account never expires (the eighth field in /etc/shadow). 4. Add the editor group to the secondary groups of christian. Assume that this group already contains emma, dave and frank as ordinary members. How can you verify that there are no administrators for this group? 196 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.1 Manage user and group accounts and related system files # cat /etc/group | grep editor editor:x:1100:emma,dave,frank # usermod -a -G editor christian # cat /etc/group | grep editor editor:x:1100:emma,dave,frank,christian # cat /etc/gshadow | grep editor editor:!::emma,dave,frank,christian The third and fourth fields in /etc/ghadow contain administrators and ordinary members for the specified group. Therefore, since the third field is empty for editor, there are no administrators for this group (emma, dave, frank and christian are all ordinary members). 5. Run the ls -l /etc/passwd /etc/group /etc/shadow /etc/gshadow command and describe the output that it gives you in terms of file permissions. Which of these four files are shadowed for security reasons? Assume your system uses shadow passwords. # ls -l /etc/passwd /etc/group /etc/shadow /etc/gshadow -rw-r--r-- 1 root root 853 mag 1 08:00 /etc/group -rw-r----- 1 root shadow 1203 mag 1 08:00 /etc/gshadow -rw-r--r-- 1 root root 1354 mag 1 08:00 /etc/passwd -rw-r----- 1 root shadow 1563 mag 1 08:00 /etc/shadow The /etc/passwd and /etc/group files are world readable and are shadowed for security reasons. When shadow passwords are used, you can see an x in the second field of these files, because the encrypted passwords for users and groups are stored in /etc/shadow and /etc/gshadow, which are readable only by root and, in my system, even by members belonging to the shadow group. Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 197 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks 107.2 Automate system administration tasks by scheduling jobs Reference to LPI objectives LPIC-1 version 5.0, Exam 102, Objective 107.2 Weight 4 Key knowledge areas Manage cron and at jobs. Configure user access to cron and at services. Understand systemd timer units. Partial list of the used files, terms and utilities /etc/cron.{d,daily,hourly,monthly,weekly}/ /etc/at.deny /etc/at.allow /etc/crontab /etc/cron.allow /etc/cron.deny /var/spool/cron/ crontab at atq atrm 198 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.2 Automate system administration tasks by scheduling jobs systemctl systemd-run Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 199 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks 107.2 Lesson 1 Certificate: LPIC-1 Version: 5.0 Topic: 107 Administrative Tasks Objective: 107.2 Automate system administration tasks by scheduling jobs Lesson: 1 of 2 Introduction One of the most important tasks of a good system administrator is to schedule jobs that must be executed on a regular basis. For example, an administrator can create and automate jobs for backups, system upgrades and to perform many other repetitive activities. To do this you can use the cron facility, which is useful to automate periodic job scheduling. Schedule Jobs with Cron In Linux, cron is a daemon that runs continuously and wakes up every minute to check a set of tables to find tasks to execute. These tables are known as crontabs and contain the so-called cron jobs. Cron is suitable for servers and systems that are constantly powered on, because each cron job is executed only if the system is running at the scheduled time. It can be used by ordinary users, each of whom has their own crontab, as well as the root user who manages the system crontabs. In Linux there is also the anacron facility, which is suitable for systems that can be NOTE powered off (such as desktops or laptops). It can only be used by root. If the 200 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.2 Automate system administration tasks by scheduling jobs machine is off when the anacron jobs must be executed, they will run the next time the machine is powered on. anacron is out of scope for the LPIC-1 certification. User Crontabs User crontabs are text files that manage the scheduling of user-defined cron jobs. They are always named after the user account that created them, but the location of these files depends on the distribution used (generally a subdirectory of /var/spool/cron). Each line in a user crontab contains six fields separated by a space: The minute of the hour (0-59). The hour of the day (0-23). The day of the month (1-31). The month of the year (1-12). The day of the week (0-7 with Sunday=0 or Sunday=7). The command to run. For the month of the year and the day of the week you can use the first three letters of the name instead of the corresponding number. The first five fields indicate when to execute the command that is specified in the sixth field, and they can contain one or more values. In particular, you can specify multiple values using: * (asterisk) Refers to any value. , (comma) Specifies a list of possible values. - (dash) Specifies a range of possible values. / (slash) Specifies stepped values. Many distributions include the /etc/crontab file which can be used as a reference for the layout of a cron file. Here is an example /etc/crontab file from a Debian installation: Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 201 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks SHELL=/bin/sh PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin # Example of job definition: #.---------------- minute (0 - 59) # |.------------- hour (0 - 23) # | |.---------- day of month (1 - 31) # | | |.------- month (1 - 12) OR jan,feb,mar,apr... # | | | |.---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat # | | | | | # * * * * * user-name command to be executed System Crontabs System crontabs are text files that manage the scheduling of system cron jobs and can only be edited by the root user. /etc/crontab and all files in the /etc/cron.d directory are system crontabs. Most distributions also include the /etc/cron.hourly, /etc/cron.daily, /etc/cron.weekly and /etc/cron.monthly directories that contain scripts to be run with the appropriate frequency. For example, if you want to run a script daily you can place it in /etc/cron.daily. Some distributions use /etc/cron.d/hourly, /etc/cron.d/daily, /etc/cron.d/weekly and /etc/cron.d/monthly. Always remember to WARNING check for the correct directories in which to place scripts you would like cron to run. The syntax of system crontabs is similar to that of user crontabs, however it also requires an additional mandatory field that specifies which user will run the cron job. Therefore, each line in a system crontab contains seven fields separated by a space: The minute of the hour (0-59). The hour of the day (0-23). The day of the month (1-31). The month of the year (1-12). The day of the week (0-7 with Sunday=0 or Sunday=7). The name of the user account to be used when executing the command. The command to run. 202 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.2 Automate system administration tasks by scheduling jobs As for user crontabs, you can specify multiple values for the time fields using the *, , , - and / operators. You may also indicate the month of the year and the day of the week with the first three letters of the name instead of the corresponding number. Particular Time Specifications When editing crontab files, you can also use special shortcuts in the first five columns instead of the time specifications: @reboot Run the specified task once after reboot. @hourly Run the specified task once an hour at the beginning of the hour. @daily (or @midnight) Run the specified task once a day at midnight. @weekly Run the specified task once a week at midnight on Sunday. @monthly Run the specified task once a month at midnight on the first day of the month. @yearly (or @annually) Run the specified task once a year at midnight on the 1st of January. Crontab Variables Within a crontab file, there are sometimes variable assignments defined before the scheduled tasks are declared. The environment variables commonly set are: HOME The directory where cron invokes the commands (by default the user’s home directory). MAILTO The name of the user or the address to which the standard output and error is mailed (by default the crontab owner). Multiple comma-separated values are also allowed and an empty value indicates that no mail should be sent. Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 203 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks PATH The path where commands can be found. SHELL The shell to use (by default /bin/sh). Creating User Cron Jobs The crontab command is used to maintain crontab files for individual users. In particular, you can run the crontab -e command to edit your own crontab file or to create one if it doesn’t already exist. $ crontab -e no crontab for frank - using an empty one Select an editor. To change later, run 'select-editor'. 1. /bin/ed 2. /bin/nano < ‑‑‑‑ easiest 3. /usr/bin/emacs24 4. /usr/bin/vim.tiny Choose 1-4 : By default, the crontab command opens the editor specified by the VISUAL or EDITOR environment variables so you can start editing your crontab file with the preferred editor. Some distributions, as shown in the example above, allow you to choose the editor from a list when crontab is run for the first time. If you want to run the foo.sh script located in your home directory every day at 10:00 am, you can add the following line to your crontab file: 0 10 * * * /home/frank/foo.sh Consider the following sample crontab entries: 0,15,30,45 08 * * 2 /home/frank/bar.sh 30 20 1-15 1,6 1-5 /home/frank/foobar.sh In the first line the bar.sh script is executed every Tuesday at 08:00 am, at 08:15 am, at 08:30 am 204 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.2 Automate system administration tasks by scheduling jobs and at 08:45 am. On the second line the foobar.sh script is executed at 08:30 pm from Monday to Friday for the first fifteen days of January and June. Although crontab files can be edited manually, it is always recommended to WARNING use the crontab command. The permissions on the crontab files usually only allow them to be edited via the crontab command. In addition to the -e option mentioned above, the crontab command has other useful options: -l Display the current crontab on standard output. -r Remove the current crontab. -u Specify the name of the user whose crontab needs to be modified. This option requires root privileges and allows the root user to edit user crontab files. Creating System Cron Jobs Unlike user crontabs, system crontabs are updated using an editor: therefore, you do not need to run the crontab command to edit /etc/crontab and the files in /etc/cron.d. Remember that when editing system crontabs, you must specify the account that will be used to run the cron job (usually the root user). For example, if you want to run the barfoo.sh script located in the /root directory every day at 01:30 am, you can open /etc/crontab with your preferred editor and add the following line: 30 01 * * * root /root/barfoo.sh >>/root/output.log 2>>/root/error.log In the above example, output of the job is appended to /root/output.log, while errors are appended to /root/error.log. Unless output is redirected to a file as in the example above (or the MAILTO variable is set to a blank value), all output from a cron job will be sent to the user via e-mail. A common practice is to redirect standard output to WARNING /dev/null (or to a file for later review if necessary) and to not redirect standard error. This way the user will be notified immediately by e-mail of any errors. Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 205 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks Configure Access to Job Scheduling In Linux the /etc/cron.allow and /etc/cron.deny files are used to set crontab restrictions. In particular, they are used to allow or disallow the scheduling of cron jobs for different users. If /etc/cron.allow exists, only non-root users listed within it can schedule cron jobs using the crontab command. If /etc/cron.allow does not exist but /etc/cron.deny exists, only non- root users listed within this file cannot schedule cron jobs using the crontab command (in this case an empty /etc/cron.deny means that each user is allowed to schedule cron jobs with crontab). If neither of these files exist, the user’s access to cron job scheduling depends on the distribution used. The /etc/cron.allow and /etc/cron.deny files contain of a list of usernames, NOTE each on a separate line. An Alternative to Cron Using systemd as the system and service manager, you can set timers as an alternative to cron to schedule your tasks. Timers are systemd unit files identified by the.timer suffix, and for each of these there must be a corresponding unit file which describes the unit to be activated when the timer elapses. By default, a timer activates a service with the same name, except for the suffix. A timer includes a [Timer] section that specifies when scheduled jobs should run. Specifically, you can use the OnCalendar= option to define real-time timers which work in the same way as cron jobs (they are based on calendar event expressions). The OnCalendar= option requires the following syntax: DayOfWeek Year-Month-Day Hour:Minute:Second with DayOfWeek being optional. The *, / and , operators have the same meaning as those used for cron jobs, while you can use.. between two values to indicate a contiguous range. For DayOfWeek specification, you can use the first three letters of the name or the full name. You can also define monotonic timers that activate after some time has elapsed NOTE from a specific start point (for example, when the machine was booted up or when the timer itself is activated). For example, if you want to run the service named /etc/systemd/system/foobar.service at 05:30 on the first Monday of each month, you can add the following lines in the corresponding /etc/systemd/system/foobar.timer unit file. 206 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.2 Automate system administration tasks by scheduling jobs [Unit] Description=Run the foobar service [Timer] OnCalendar=Mon *-*-1..7 05:30:00 Persistent=true [Install] WantedBy=timers.target Once you have created the new timer, you can enable it and start it by running the following commands as root: # systemctl enable foobar.timer # systemctl start foobar.timer You can change the frequency of your scheduled job, modifying the OnCalendar value and then typing the systemctl daemon-reload command. Finally, if you want to view the list of active timers sorted by the time they elapse next, you can use the systemctl list-timers command. You can add the --all option to see the inactive timer units as well. Remember that timers are logged to the systemd journal and you can review the logs of the different units using the journalctl command. Also remember that if NOTE you are acting as an ordinary user, you need to use the --user option of the systemctl and journalctl commands. Instead of the longer normalized form mentioned above, you can use some special expressions which describe particular frequencies for job execution: hourly Run the specified task once an hour at the beginning of the hour. daily Run the specified task once a day at midnight. weekly Run the specified task once a week at midnight on Monday. Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 207 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks monthly Run the specified task once a month at midnight on the first day of the month. yearly Run the specified task once a year at midnight on the first day of January. You can see the manual pages for the full list of time and date specifications at systemd.timer(5). 208 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.2 Automate system administration tasks by scheduling jobs Guided Exercises 1. For each of the following crontab shortcuts, indicate the corresponding time specification (i.e. the first five columns in a user crontab file): @hourly @daily @weekly @monthly @annually 2. For each of the following OnCalendar shortcuts, indicate the corresponding time specification (the longer normalized form): hourly daily weekly monthly yearly 3. Explain the meaning of the following time specifications found in a crontab file: 30 13 * * 1-5 00 09-18 * * * 30 08 1 1 * 0,20,40 11 * * Sun 00 09 10-20 1-3 * */20 * * * * 4. Explain the meaning of the following time specifications used in the OnCalendar option of a timer file: *-*-* 08:30:00 Sat,Sun *-*-* 05:00:00 Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 209 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks *-*-01 13:15,30,45:00 Fri *-09..12-* 16:20:00 Mon,Tue *-*-1,15 08:30:00 *-*-* *:00/05:00 210 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.2 Automate system administration tasks by scheduling jobs Explorational Exercises 1. Assuming that you are authorized to schedule jobs with cron as an ordinary user, what command would you use to to create your own crontab file? 2. Create a simple scheduled job that executes the date command every Friday at 01:00 pm. Where can you see the output of this job? 3. Create another scheduled job that executes the foobar.sh script every minute, redirecting the output to the output.log file in your home directory so that only standard error is sent to you by e-mail. 4. Look at the crontab entry of the newly created scheduled job. Why is it not necessary to specify the absolute path of the file in which the standard output is saved? And why can you use the./foobar.sh command to execute the script? 5. Edit the previous crontab entry by removing the output redirection and disable the first cron job you have created. 6. How can you send the output and errors of your scheduled job to the emma user account via e- mail? And how can you avoid sending the standard output and error via e-mail? 7. Execute the command ls -l /usr/bin/crontab. Which special bit is set and what is its meaning? Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 211 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks Summary In this lesson, you learned: Use cron to run jobs at regular intervals. Manage cron jobs. Configure user access to cron job scheduling. Understand the role of systemd timer units as an alternative to cron. The following commands and files were discussed in this lesson: crontab Maintain crontab files for individual users. /etc/cron.allow and /etc/cron.deny Particular files used to set crontab restrictions. /etc/crontab System crontab file. /etc/cron.d The directory that contains system crontab files. systemctl Control the systemd system and service manager. In relation to timers, it can be used to enable and start them. 212 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.2 Automate system administration tasks by scheduling jobs Answers to Guided Exercises 1. For each of the following crontab shortcuts, indicate the corresponding time specification (the first five columns in a crontab file): @hourly 0 * * * * @daily 0 0 * * * @weekly 0 0 * * 0 @monthly 0 0 1 * * @annually 0 0 1 1 * 2. For each of the following OnCalendar shortcuts, indicate the corresponding time specification (the longer normalized form): hourly *-*-* *:00:00 daily *-*-* 00:00:00 weekly Mon *-*-* 00:00:00 monthly *-*-01 00:00:00 yearly *-01-01 00:00:00 3. Explain the meaning of the following time specifications for a crontab file: 30 13 * * 1-5 At 01:30 pm every day of the week from Monday to Friday 00 09-18 * * * Every day and every hour from 09 am to 06 pm 30 08 1 1 * At 08:30 am on the first day of January 0,20,40 11 * * Sun Every Sunday at 11:00 am, 11:20 am and 11:40 am 00 09 10-20 1-3 * At 09:00 am from the 10th to the 20th of January, February and March */20 * * * * Every twenty minutes 4. Explain the meaning of the following time specifications used in the OnCalendar option of a timer file: Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 213 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks *-*-* 08:30:00 Every day at 08:30 am Sat,Sun *-*-* 05:00:00 At 05:00 am on Saturday and Sunday *-*-01 13:15,30,45:00 At 01:15 pm, 01:30 pm and 01:45 pm on the first day of the month Fri *-09..12-* 16:20:00 At 04:20 pm every Friday in September, October, November and December Mon,Tue *-*-1,15 08:30:00 At 08.30 am on the first or fifteenth day of each month only if the day is a Monday or Tuesday *-*-* *:00/05:00 Every five minutes 214 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.2 Automate system administration tasks by scheduling jobs Answers to Explorational Exercises 1. Assuming that you are authorized to schedule jobs with cron as an ordinary user, what command would you use to to create your own crontab file? dave@hostname ~ $ crontab -e no crontab for dave - using an empty one Select an editor. To change later, run 'select-editor'. 1. /bin/ed 2. /bin/nano < ---- easiest 3. /usr/bin/emacs24 4. /usr/bin/vim.tiny Choose 1-4 : 2. Create a simple scheduled job that executes the date command every Friday at 01:00 pm. Where can you see the output of this job? 00 13 * * 5 date The output is mailed to the user; to view it, you can use the mail command. 3. Create another scheduled job that executes the foobar.sh script every minute, redirecting the output to the output.log file in your home directory so that only standard error is sent to you by e-mail. */1 * * * *./foobar.sh >> output.log 4. Look at the crontab entry of the newly created scheduled job. Why is it not necessary to specify the absolute path of the file in which the standard output is saved? And why can you use the./foobar.sh command to execute the script? cron invokes the commands from the user’s home directory, unless another location is specified by the HOME environment variable within the crontab file. For this reason, you can use the relative path of the output file and run the script with./foobar.sh. 5. Edit the previous crontab entry by removing the output redirection and disable the first cron job you have created. Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 215 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks #00 13 * * 5 date */1 * * * *./foobar.sh To disable a cron job, you can simply comment the corresponding line within the crontab file. 6. How can you send the output and errors of your scheduled job to the emma user account via e- mail? And how can you avoid sending the standard output and error via e-mail? To send the standard output and error to emma, you must set the MAILTO environment variable in your crontab file as follows: MAILTO="emma" To tell cron that no mail should be sent, you can assign an empty value to the MAILTO environment variable. MAILTO="" 7. Execute the command ls -l /usr/bin/crontab. Which special bit is set and what is its meaning? $ ls -l /usr/bin/crontab -rwxr-sr-x 1 root crontab 25104 feb 10 2015 /usr/bin/crontab The crontab command has the SGID bit set (the s character instead of the executable flag for the group), which means that it is executed with the privileges of the group (thus crontab). This is why ordinary users can edit their crontab file using the crontab command. Note that many distributions have file permissions set such that crontab files can only be edited via the crontab command. 216 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.2 Automate system administration tasks by scheduling jobs 107.2 Lesson 2 Certificate: LPIC-1 Version: 5.0 Topic: 107 Administrative Tasks Objective: 107.2 Automate system administration tasks by scheduling jobs Lesson: 2 of 2 Introduction As you learned in the previous lesson, you can schedule regular jobs using cron or systemd timers, but sometimes you may need to run a job at a specific time in the future only once. To do this, you can use another powerful utility: the at command. Schedule Jobs with at The at command is used for one-time task scheduling and only requires that you specify when the job should be run in the future. After entering at on the command line followed by the time specification, you will enter the at prompt where you can define the commands to be executed. You can exit the prompt with the Ctrl + D key-sequence. $ at now +5 minutes warning: commands will be executed using /bin/sh at> date at> Ctrl+D Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 217 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks job 12 at Sat Sep 14 09:15:00 2019 The at job in the above example simply executes the date command after five minutes. Similar to cron, the standard output and error is sent to you via e-mail. Note that the atd daemon will need to be running on the system in order for you to use at job scheduling. In Linux, the batch command is similar to at, however batch jobs are executed NOTE only when the system load is low enough to allow it. The most important options which apply to the at command are: -c Print the commands of a specific job ID to the standard output. -d Delete jobs based on their job ID. It is an alias for atrm. -f Read the job from a file instead of the standard input. -l List the pending jobs of the user. If the user is root, all jobs of all users are listed. It is an alias for atq. -m Send mail to the user at the end of the job even if there was no output. -q Specify a queue in the form of a single letter from a to z and from A to Z (by default a for at and b for batch). Jobs in the queues with the highest letters are executed with increased niceness. Jobs submitted to a queue with a capital letter are treated as batch jobs. -v Show the time at which the job will run before reading the job. List Scheduled Jobs with atq Now let us schedule two more at jobs: the first executes the foo.sh script at 09:30 am, while the second executes the bar.sh script after one hour. 218 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.2 Automate system administration tasks by scheduling jobs $ at 09:30 AM warning: commands will be executed using /bin/sh at>./foo.sh at> Ctrl+D job 13 at Sat Sep 14 09:30:00 2019 $ at now +2 hours warning: commands will be executed using /bin/sh at>./bar.sh at> Ctrl+D job 14 at Sat Sep 14 11:10:00 2019 To list your pending jobs, you can use the atq command which shows the following information for each job: job ID, job execution date, job execution time, queue, and username. $ atq 14 Sat Sep 14 11:10:00 2019 a frank 13 Sat Sep 14 09:30:00 2019 a frank 12 Sat Sep 14 09:15:00 2019 a frank Remember that the at -l command is an alias for atq. NOTE If you run atq as root, it will display the queued jobs for all users. Delete Jobs with atrm If you want to delete an at job, you can use the atrm command followed by the job ID. For example, to delete the job with ID 14, you can run the following: $ atrm 14 You can delete multiple jobs with atrm by specifying multiple IDs separated by spaces. Remember that the at -d command is an alias for atrm. NOTE If you run atrm as root you can delete the jobs of all users. Configure Access to Job Scheduling Authorization for ordinary users to schedule at jobs is determined by the /etc/at.allow and /etc/at.deny files. If /etc/at.allow exists, only non-root users listed within it can schedule at jobs. If /etc/at.allow does not exist but /etc/at.deny exists, only non-root users listed within Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 219 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks it cannot schedule at jobs (in this case an empty /etc/at.deny file means that each user is allowed to schedule at jobs). If neither of these files exist, the user’s access to at job scheduling depends on the distribution used. Time Specifications You can specify when to execute a particular at job using the form HH:MM, optionally followed by AM or PM in case of 12-hour format. If the specified time has already passed, the next day is assumed. If you want to schedule a particular date on which the job will run, you must add the date information after the time using one of the following forms: month-name day-of-month, month-name day-of-month year, MMDDYY, MM/DD/YY, DD.MM.YY and YYYY-MM-DD). The following keywords are also accepted: midnight, noon, teatime (4 pm) and now followed by a plus sign (+) and a time period (minutes, hours, days and weeks). Finally, you can tell at to run the job today or tomorrow by suffixing the time with the words today or tomorrow. For example, you can use at 07:15 AM Jan 01 to execute a job at 07:15 am on 01 January and at now +5 minutes to execute a job five minutes from now. You can read the timespec file under the /usr/share tree for more information about the exact definition of time specifications. An Alternative to at Using systemd as the system and service manager, you can also schedule one-time tasks with the systemd-run command. It is typically used to create a transient timer unit so that a command will be executed at a specific time without the need to create a service file. For example, acting as root, you can run the date command at 11:30 AM on 2019/10/06 using the following: # systemd-run --on-calendar='2019-10-06 11:30' date If you want to run the foo.sh script, located in your current working directory, after two minutes you can use: # systemd-run --on-active="2m"./foo.sh Consult the manual pages to learn all possible uses of systemd-run with systemd-run(1). Remember that timers are logged to the systemd journal and you can review the logs of the different units using the journalctl command. Also remember that if NOTE you are acting as an ordinary user, you need to use the --user option of the systemd-run and journalctl commands. 220 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.2 Automate system administration tasks by scheduling jobs Guided Exercises 1. For each of the following time specifications, indicate which is valid and which is invalid for at: at 08:30 AM next week at midday at 01-01-2020 07:30 PM at 21:50 01.01.20 at now +4 days at 10:15 PM 31/03/2021 at tomorrow 08:30 AM 2. Once you have scheduled a job with at, how can you review its commands? 3. Which commands can you use to review your pending at jobs? Which commands would you use to delete them? 4. With systemd, which command is used as an alternative to at? Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 221 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks Explorational Exercises 1. Create an at job that runs the foo.sh script, located in your home directory, at 10:30 am on coming October 31st. Assume you are acting as an ordinary user. 2. Login to the system as another ordinary user and create another at job that runs the bar.sh script tomorrow at 10:00 am. Assume the script is located in the user’s home directory. 3. Login to the system as another ordinary user and create another at job that runs the foobar.sh script just after 30 minutes. Assume the script is located in the user’s home directory. 4. Now as root, run the atq command to review the scheduled at jobs of all users. What happens if an ordinary user executes this command? 5. As root, delete all these pending at jobs using a single command. 6. Run the ls -l /usr/bin/at command and examine its permissions. 222 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.2 Automate system administration tasks by scheduling jobs Summary In this lesson, you learned: Use at to run one-time jobs at a specific time. Manage at jobs. Configure user access to at job scheduling. Use systemd-run as an alternative to at. The following commands and files were discussed in this lesson: at Execute commands at a specified time. atq List the user’s pending at jobs, unless the user is the superuser. atrm Delete at jobs, identified by their job number. /etc/at.allow and /etc/at.deny Particular files used to set at restrictions. systemd-run Create and start a transient timer unit as an alternative to at for one-time scheduling. Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 223 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks Answers to Guided Exercises 1. For each of the following time specifications, indicate which is valid and which is invalid for at: at 08:30 AM next week Valid at midday Invalid at 01-01-2020 07:30 PM Invalid at 21:50 01.01.20 Valid at now +4 days Valid at 10:15 PM 31/03/2021 Invalid at tomorrow 08:30 AM monotonic Invalid 2. Once you have scheduled a job with at, how can you review its commands? You can use the at -c command followed by the ID of the job whose commands you want to review. Note that the output also contains most of the environment that was active at the time the job was scheduled. Remember that root can review the jobs of all users. 3. Which commands can you use to review your pending at jobs? Which commands would you use to delete them? You can use the at -l command to review your pending jobs, and you can use the at -d command to delete your jobs. at -l is an alias for atq and at -d is an alias for atrm. Remember that root can list and delete the jobs of all users. 4. With systemd, which command is used as an alternative to at? The systemd-run command can be used as an alternative to at to schedule one-time jobs. For example, you can use it to run commands at a specific time, defining a calendar timer or a monotonic timer relative to different starting points. 224 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.2 Automate system administration tasks by scheduling jobs Answers to Explorational Exercises 1. Create an at job that runs the foo.sh script, located in your home directory, at 10:30 am on coming October 31st. Assume you are acting as an ordinary user. $ at 10:30 AM October 31 warning: commands will be executed using /bin/sh at>./foo.sh at> Ctrl+D job 50 at Thu Oct 31 10:30:00 2019 2. Login to the system as another ordinary user and create another at job that runs the bar.sh script tomorrow at 10:00 am. Assume the script is located in the user’s home directory. $ at 10:00 AM tomorrow warning: commands will be executed using /bin/sh at>./bar.sh at> Ctrl+D job 51 at Sun Oct 6 10:00:00 2019 3. Login to the system as another ordinary user and create another at job that runs the foobar.sh script just after 30 minutes. Assume the script is located in the user’s home directory. $ at now +30 minutes warning: commands will be executed using /bin/sh at>./foobar.sh at> Ctrl+D job 52 at Sat Oct 5 10:19:00 2019 4. Now as root, run the atq command to review the scheduled at jobs of all users. What happens if an ordinary user executes this command? # atq 52 Sat Oct 5 10:19:00 2019 a dave 50 Thu Oct 31 10:30:00 2019 a frank 51 Sun Oct 6 10:00:00 2019 a emma If you run the atq command as root, all pending at jobs of all users are listed. If you run it as Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 225 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks an ordinary user, only your own pending at jobs are listed. 5. As root, delete all of these pending at jobs using a single command. # atrm 50 51 52 6. As root, run the ls -l /usr/bin/at command and examine its permissions. # ls -l /usr/bin/at -rwsr-sr-x 1 daemon daemon 43762 Dec 1 2015 /usr/bin/at In this distribution, the at command has both the SUID (the s character instead of the executable flag for the owner) and SGID (the s character instead of the executable flag for the group) bits set, which means that it is executed with the privileges of the owner and group of the file (daemon for both). This is why ordinary users are able to schedule jobs with at. 226 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.3 Localisation and internationalisation 107.3 Localisation and internationalisation Reference to LPI objectives LPIC-1 version 5.0, Exam 102, Objective 107.3 Weight 3 Key knowledge areas Configure locale settings and environment variables. Configure timezone settings and environment variables. Partial list of the used files, terms and utilities /etc/timezone /etc/localtime /usr/share/zoneinfo/ LC_* LC_ALL LANG TZ /usr/bin/locale tzselect timedatectl date iconv Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 227 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks UTF-8 ISO-8859 ASCII Unicode 228 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.3 Localisation and internationalisation 107.3 Lesson 1 Certificate: LPIC-1 Version: 5.0 Topic: 107 Administrative Tasks Objective: 107.3 Localisation and internationalisation Lesson: 1 of 1 Introduction All major Linux distributions can be configured to use custom localisation settings These settings include region and language related definitions such as the time zone, interface language as well as character encoding can be modified during the installation of the operating system or anytime after that. Applications rely on environment variables, system configuration files and commands to decide the proper time and language to use; hence most Linux distribution share a standardized way to adjust time and localisation settings. These adjustments are important not only to improve user experience, but also to ensure that the timing of system events — important, for example, for reporting security related issues — are correctly calculated. To be able to represent any written text, regardless of the spoken language, modern operating systems need a reference character encoding standard, and Linux systems are no different. As computers are only able to deal with numbers, a text character is nothing more than a number associated with a graphic symbol. Distinct computer platforms may associate distinct number values to the same character, so a common character encoding standard is necessary to make them compatible. A text document created in one system will be readable in another system only Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 229 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks if both agree on the encoding format and on what number is associated to what character, or at least if they know how to convert between the two standards. The heterogeneous nature of the localisation settings in Linux-based systems result in subtle differences between the distributions. Despite these differences, all distributions share the same basic tools and concepts to setup the internationalisation aspects of a system. Time Zones Time zones are roughly proportional discrete bands of Earth’s surface spanning the equivalent to one hour, that is, regions of the world experiencing the same hour of the day at any given time. Since there is not a single longitude that can be considered as the beginning of the day for the whole world, time zones are relative to the prime meridian, where the Earth’s longitude angle is defined to be 0. The time at the prime meridian is called the Coordinated Universal Time, by convention abbreviated to UTC. Due to practical reasons, time zones do not follow the exact longitudinal distance from the reference point (the prime meridian). Instead, time zones are artificially adapted to follow the borders of countries or other significant subdivisions. The political subdivisions are so relevant that time zones are named after some major geographical agent in that particular area, usually based on the name of a large country or city inside the zone. Yet, time zones are divided according to their time offset relative to UTC and this offset can also be used to indicate the zone in question. The time zone GMT-5, for example, indicates a region for which UTC time is five hours ahead, i.e. that region is 5 hours behind UTC. Likewise, the time zone GMT+3 indicates a region for which UTC time is three hours behind. The term GMT — from Greenwich Mean Time — is used as a synonym for UTC in the offset based zone names. A connected machine can be accessed from different parts of the world, so it is a good practice to set the hardware clock to UTC (the GMT+0 time zone) and leave the choice of the time zone to each particular case. Cloud services, for example, are commonly configured to use UTC, as it can help to mitigate occasional inconsistencies between local time and time at clients or at other servers. In contrast, users who open a remote session on the server may want to use their local time zone. Thus, it will be up to the operating system to set up the correct time zone according to each case. In addition to the current date and time, command date will also print the currently configured time zone: $ date Mon Oct 21 10:45:21 -03 2019 230 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.3 Localisation and internationalisation The offset relative to UTC is given by the -03 value, meaning that the displayed time is three hours less than UTC. Therefore, UTC time is three hours ahead, making GMT-3 the corresponding time zone for the given time. Command timedatectl, which is available in distributions using systemd, shows more details about the system time and date: $ timedatectl Local time: Sat 2019-10-19 17:53:18 -03 Universal time: Sat 2019-10-19 20:53:18 UTC RTC time: Sat 2019-10-19 20:53:18 Time zone: America/Sao_Paulo (-03, -0300) System clock synchronized: yes systemd-timesyncd.service active: yes RTC in local TZ: no As shown in the Time zone entry, time zone names based on localities — like America/Sao_Paulo — are also accepted. The default time zone for the system is kept in the file /etc/timezone, either by the zone’s full descriptive name or offset. Generic time zone names given by the UTC offset must include Etc as the first part of the name. So, to set the default time zone to GMT+3, the name of the time zone must be Etc/GMT+3: $ cat /etc/timezone Etc/GMT+3 Although time zone names based on localities do not require the time offset to work, they are not so straight forward to choose from. The same zone can have more than one name, which can make it difficult to remember. In order to ease this issue, command tzselect offers an interactive method which will guide the user towards the correct time zone definition. Command tzselect should be available by default in all Linux distributions, as it is provided by the package that contains necessary utility programs related to the GNU C Library. Command tzselect will be useful, for example, for a user who wants to identify the time zone for “São Paulo City” in “Brazil”. tzselect starts by asking the macro region of the desired location: $ tzselect Please identify a location so that time zone rules can be set correctly. Please select a continent, ocean, "coord", or "TZ". 1) Africa 2) Americas 3) Antarctica Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 231 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks 4) Asia 5) Atlantic Ocean 6) Australia 7) Europe 8) Indian Ocean 9) Pacific Ocean 10) coord - I want to use geographical coordinates. 11) TZ - I want to specify the time zone using the Posix TZ format. #? 2 Option 2 is for (North and South) American locations, not necessarily in the same time zone. It is also possible to specify the time zone with geographical coordinates or with the offset notation, also known as the Posix TZ format. The next step is to choose the country: Please select a country whose clocks agree with yours. 1) Anguilla 19) Dominican Republic 37) Peru 2) Antigua & Barbuda 20) Ecuador 38) Puerto Rico 3) Argentina 21) El Salvador 39) St Barthelemy 4) Aruba 22) French Guiana 40) St Kitts & Nevis 5) Bahamas 23) Greenland 41) St Lucia 6) Barbados 24) Grenada 42) St Maarten (Dutch) 7) Belize 25) Guadeloupe 43) St Martin (French) 8) Bolivia 26) Guatemala 44) St Pierre & Miquelon 9) Brazil 27) Guyana 45) St Vincent 10) Canada 28) Haiti 46) Suriname 11) Caribbean NL 29) Honduras 47) Trinidad & Tobago 12) Cayman Islands 30) Jamaica 48) Turks & Caicos Is 13) Chile 31) Martinique 49) United States 14) Colombia 32) Mexico 50) Uruguay 15) Costa Rica 33) Montserrat 51) Venezuela 16) Cuba 34) Nicaragua 52) Virgin Islands (UK) 17) Curaçao 35) Panama 53) Virgin Islands (US) 18) Dominica 36) Paraguay #? 9 Brazil’s territory spans four time zones, so the country information alone is not enough to set the time zone. In the next step tzselect will require the user to specify the local region: Please select one of the following time zone regions. 1) Atlantic islands 2) Pará (east); Amapá 3) Brazil (northeast: MA, PI, CE, RN, PB) 232 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.3 Localisation and internationalisation 4) Pernambuco 5) Tocantins 6) Alagoas, Sergipe 7) Bahia 8) Brazil (southeast: GO, DF, MG, ES, RJ, SP, PR, SC, RS) 9) Mato Grosso do Sul 10) Mato Grosso 11) Pará (west) 12) Rondônia 13) Roraima 14) Amazonas (east) 15) Amazonas (west) 16) Acre #? 8 Not all locality names are available, but choosing the closest region will be good enough. The given information will then be used by tzselect to display the corresponding time zone: The following information has been given: Brazil Brazil (southeast: GO, DF, MG, ES, RJ, SP, PR, SC, RS) Therefore TZ='America/Sao_Paulo' will be used. Selected time is now: sex out 18 18:47:07 -03 2019. Universal Time is now: sex out 18 21:47:07 UTC 2019. Is the above information OK? 1) Yes 2) No #? 1 You can make this change permanent for yourself by appending the line TZ='America/Sao_Paulo'; export TZ to the file '.profile' in your home directory; then log out and log in again. Here is that TZ value again, this time on standard output so that you can use the /usr/bin/tzselect command in shell scripts: America/Sao_Paulo The resulting time zone name, America/Sao_Paulo, can also be used as the content of the /etc/timezone to inform the default time zone for the system: Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 233 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks $ cat /etc/timezone America/Sao_Paulo As stated by the output of tzselect, the environment variable TZ defines the time zone for the shell session, whatever the system’s default time zone is. Adding the line TZ='America/Sao_Paulo'; export TZ to the file ~/.profile will make America/Sao_Paulo the time zone for the user’s future sessions. The TZ variable can also be temporarily modified during the current session, in order to display the time in a different time zone: $ env TZ='Africa/Cairo' date Mon Oct 21 15:45:21 EET 2019 In the example, command env will run the given command in a new sub-shell session with the same environment variables of the current session, except for the variable TZ, modified by the argument TZ='Africa/Cairo'. Daylight Savings Time Many regions adopt daylight savings time for part of the year — when clocks are typically adjusted by an hour — that could lead a misconfigured system to report the wrong time during that season of the year. The /etc/localtime file contains the data used by the operating system to adjust its clock accordingly. Standard Linux systems have files for all time zones in the directory /usr/share/zoneinfo/, so /etc/localtime is just a symbolic link to the actual data file inside that directory. The files in /usr/share/zoneinfo/ are organized by the name of the corresponding time zone, so the data file for the America/Sao_Paulo time zone will be /usr/share/zoneinfo/America/Sao_Paulo As the definitions for the daylight savings time may change, it is important to keep the files in /usr/share/zoneinfo/ up to date. The upgrade command of the package management tool provided by the distribution should update them every time a new version is available. Language and Character Encoding Linux systems can work with a wide variety of languages and non-western character encodings, definitions known as locales. The most basic locale configuration is the definition of the environment variable LANG, from which most shell programs identify the language to use. 234 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.3 Localisation and internationalisation The content of the LANG variable follows the format ab_CD, where ab is the language code and CD is the region code. The language code should follow the ISO-639 standard and the region code should follow the ISO-3166 standard. A system configured to use Brazilian Portuguese, for example, should have the LANG variable defined to pt_BR.UTF-8: $ echo $LANG pt_BR.UTF-8 As seen in the sample output, the LANG variable also holds the character encoding intended for the system. ASCII, short for American Standard Code for Information Interchange, was the first widely used character encoding standard for electronic communication. However, since ASCII has a very limited range of available numerical values and it was based on the English alphabet, it does not contain characters used by other languages or an extended set of non-alphabetical symbols. The UTF-8 encoding is a Unicode Standard for the ordinary western characters, plus many other non- conventional symbols. As stated by the Unicode Consortium, the maintainer of the Unicode Standard, it should be adopted by default to ensure compatibility between computer platforms: The Unicode Standard provides a unique number for every character, no matter what platform, device, application or language. It has been adopted by all modern software providers and now allows data to be transported through many different platforms, devices and applications without corruption. Support of Unicode forms the foundation for the representation of languages and symbols in all major operating systems, search engines, browsers, laptops, and smart phones — plus the Internet and World Wide Web (URLs, HTML, XML, CSS, JSON, etc.). (…) the Unicode Standard and the availability of tools supporting it are among the most significant recent global software technology trends. — The Unicode Consortium, What is Unicode? Some systems may still use ISO defined standards — like the ISO-8859-1 standard — for the encoding of non-ASCII characters. However, such character encoding standards should be deprecated in favor of Unicode encodings standards. Nevertheless, all major operating systems tend to adopt the Unicode standard by default. System wide locale settings are configured in the file /etc/locale.conf. Variable LANG and other locale related variables are assigned in this file like an ordinary shell variable, for example: $ cat /etc/locale.conf LANG=pt_BR.UTF-8 Users can use a custom locale configuration by redefining the LANG environment variable. It can Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 235 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks be done for the current session only or for future sessions, by adding the new definition to the user’s Bash profile in ~/.bash_profile or ~/.profile. Until the user logs in, however, the default system locale will still be used by user independent programs, like the display manager’s login screen. The command localectl, available on systems employing systemd as the system TIP manager, can also be used to query and change the system locale. For example: localectl set-locale LANG=en_US.UTF-8. In addition to the LANG variable, other environment variables have an affect on specific locale aspects, like which currency symbol to use or the correct thousand separator for numbers: LC_COLLATE Sets the alphabetical ordering. One of its purposes is to define the order files and directories are listed. LC_CTYPE Sets how the system will treat certain sets of characters. It defines, for example, which characters to consider as uppercase or lowercase. LC_MESSAGES Sets the language to display program messages (mostly GNU programs). LC_MONETARY Sets the money unit and currency format. LC_NUMERIC Sets the numerical format for non-monetary values. Its main purpose is to define the thousand and decimal separators. LC_TIME Sets the time and date format. LC_PAPER Sets the standard paper size. LC_ALL Overrides all other variables, including LANG. The locale command will show all defined variables in the current locale configuration: 236 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.3 Localisation and internationalisation $ locale LANG=pt_BR.UTF-8 LC_CTYPE="pt_BR.UTF-8" LC_NUMERIC=pt_BR.UTF-8 LC_TIME=pt_BR.UTF-8 LC_COLLATE="pt_BR.UTF-8" LC_MONETARY=pt_BR.UTF-8 LC_MESSAGES="pt_BR.UTF-8" LC_PAPER=pt_BR.UTF-8 LC_NAME=pt_BR.UTF-8 LC_ADDRESS=pt_BR.UTF-8 LC_TELEPHONE=pt_BR.UTF-8 LC_MEASUREMENT=pt_BR.UTF-8 LC_IDENTIFICATION=pt_BR.UTF-8 LC_ALL= The only undefined variable is LC_ALL, which can be used to temporarily override all the other locale settings. The following example shows how the date command — running in a system configured to pt_BR.UTF-8 locale — will modify its output to comply with the new LC_ALL variable: $ date seg out 21 10:45:21 -03 2019 $ env LC_ALL=en_US.UTF-8 date Mon Oct 21 10:45:21 -03 2019 The modification of the LC_ALL variable made both abbreviations for the day of the week and month name to be shown in American English (en_US). It is not mandatory, however, to set the same locale for all variables. It is possible, for example, to have the language defined to pt_BR and the numerical format (LC_NUMERIC) set to the American standard. Some localisation settings change how programs deal with alphabetical ordering and number formats. Whilst conventional programs are usually prepared to correctly choose a common locale for such situations, scripts can behave unexpectedly when trying to correctly alphabetically order a list of items, for example. For this reason, it is recommended to set the environment variable LANG to the common C locale, as in LANG=C, so the script produces unambiguous results, regardless the localisation definitions used in the system where it is executed. The C locale only conducts a simple bytewise comparison, so it will also perform better than the others. Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 237 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks Encoding Conversion Text may appear with unintelligible characters when displayed on a system with a character encoding configuration other than the system where the text was created. The command iconv can be used to solve this issue, by converting the file from its original character encoding to the desired one. For example, to convert a file named original.txt from the ISO-8859-1 encoding to the file named converted.txt using UTF-8 encoding, the following command can be used: $ iconv -f ISO-8859-1 -t UTF-8 original.txt > converted.txt The option -f ISO-8859-1 (or --from-code=ISO-8859-1) sets the encoding of the original file and option -t UTF-8 (or --to-code=UTF-8) sets the encoding for the converted file. All encoding supported by command iconv are listed with command iconv -l or iconv --list. Instead of using the output redirection, like in the example, option -o converted.txt or --output converted.txt could also be used. 238 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.3 Localisation and internationalisation Guided Exercises 1. Based on the following output of the command date, what is the time zone of the system in GMT notation? $ date Mon Oct 21 18:45:21 +05 2019 2. To what file should the symbolic link /etc/localtime point to in order to make Europe/Brussels the system’s default local time? 3. Characters in text files may not be rendered correctly in a system with a character encoding different from that used in the text document. How could iconv be used to convert the WINDOWS-1252 encoded file old.txt to the file new.txt using UTF-8 encoding? Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 239 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks Explorational Exercises 1. What command will make Pacific/Auckland the default time zone for the current shell session? 2. Command uptime shows, among other things, the load average of the system in fractional numbers. It uses the current locale settings to decide if the decimal place separator should be a dot or a comma. If, for example, the current locale is set to de_DE.UTF-8 (the standard locale of Germany), uptime will use a comma as the separator. Knowing that in the American English language the dot is used as the separator, what command will make uptime display the fractions using a dot instead of a comma for the rest of the current session? 3. Command iconv will replace all characters outside the target character set with a question mark. If //TRANSLIT is appended to the target encoding, characters not represented in the target character set will be replaced (transliterated) by one or more similar looking characters. How could this method be used to convert a UTF-8 text file named readme.txt to a plain ASCII file named ascii.txt? 240 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.3 Localisation and internationalisation Summary This lesson covers how to set up a Linux system to work with custom languages and time settings. Character encoding concepts and settings are also covered, as they are very important to correctly render text content. The lesson goes through the following topics: How Linux systems select the language to display shell messages. Understanding how time zones affect the local time. How to identify the appropriate time zone and modify system settings accordingly. What character encodings are and how to convert between them. The commands and procedures addressed were: Locale and time related environment variables, such as LC_ALL, LANG and TZ. /etc/timezone /etc/localtime /usr/share/zoneinfo/ locale tzselect timedatectl date iconv Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 241 LPIC-1 (102) (Version 5.0) | Topic 107: Administrative Tasks Answers to Guided Exercises 1. Based on the following output of the command date, what is the time zone of the system in GMT notation? $ date Mon Oct 21 18:45:21 +05 2019 It’s the Etc/GMT+5 time zone. 2. To what file should the symbolic link /etc/localtime point to in order to make Europe/Brussels the system’s default local time? The link /etc/localtime should point to /usr/share/zoneinfo/Europe/Brussels. 3. Characters in text files may not be rendered correctly in a system with a character encoding different from that used in the text document. How could iconv be used to convert the WINDOWS-1252 encoded file old.txt to the file new.txt using UTF-8 encoding? Command iconv -f WINDOWS-1252 -t UTF-8 -o new.txt old.txt will perform the desired conversion. 242 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 107.3 Localisation and internationalisation Answers to Explorational Exercises 1. What command will make Pacific/Auckland the default time zone for the current shell session? export TZ=Pacific/Auckland 2. Command uptime shows, among other things, the load average of the system in fractional numbers. It uses the current locale settings to decide if the decimal place separator should be a dot or a comma. If, for example, the current locale is set to de_DE.UTF-8 (the standard locale of Germany), uptime will use a comma as the separator. Knowing that in the American English language the dot is used as the separator, what command will make uptime display the fractions using a dot instead of a comma for the rest of the current session? The command export LC_NUMERIC=en_US.UTF-8 or export LC_ALL=en_US.UTF-8. 3. Command iconv will replace all characters outside the target character set with a question mark. If //TRANSLIT is appended to the target encoding, characters not represented in the target character set will be replaced (transliterated) by one or more similar looking characters. How this method can be used to convert a UTF-8 text file named readme.txt to a plain ASCII file named ascii.txt? Command iconv -f UTF-8 -t ASCII//TRANSLIT -o ascii.txt readme.txt will perform the desired conversion. Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 243 LPIC-1 (102) (Version 5.0) | Topic 108: Essential System Services Topic 108: Essential System Services 244 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 108.1 Maintain system time 108.1 Maintain system time Reference to LPI objectives LPIC-1 version 5.0, Exam 102, Objective 108.1 Weight 3 Key knowledge areas Set the system date and time. Set the hardware clock to the correct time in UTC. Configure the correct timezone. Basic NTP configuration using ntpd and chrony. Knowledge of using the pool.ntp.org service. Awareness of the ntpq command. Partial list of the used files, terms and utilities /usr/share/zoneinfo/ /etc/timezone /etc/localtime /etc/ntp.conf /etc/chrony.conf date hwclock timedatectl Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 245 LPIC-1 (102) (Version 5.0) | Topic 108: Essential System Services ntpd ntpdate chronyc pool.ntp.org 246 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 108.1 Maintain system time 108.1 Lesson 1 Certificate: LPIC-1 (102) Version: 5.0 Topic: 108 Essential System Services Objective: 108.1 Maintain system time Lesson: 1 of 2 Introduction Accurate timekeeping is absolutely crucial for modern computing. The implementation of keeping time, however, is surprisingly complex. The practice of keeping time seems trivial to an end-user, but the system needs to be able to handle many idiosyncrasies and edge cases intelligently. Consider that time zones are not static, but may be changed by an administrative or political decision. A country may choose to stop observing Daylight Savings Time. Any program must be able to handle those changes logically. Fortunately for system administrators, the solutions for timekeeping on the Linux operating system are mature, robust and usually work without much interference. When a Linux computer boots up, it starts keeping time. We refer to this as a system clock, since it is updated by the operating system. In addition, modern computers will also have a hardware or real time clock. This hardware clock is often a feature of the motherboard and keeps time regardless if the computer is running or not. During boot, the system time is set from the hardware clock, but for the most part these two clocks run independently of each other. In this lesson we will be discussing methods of interacting with both the system and hardware clocks. On most modern Linux systems, system time and hardware time are synchronised to network Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 247 LPIC-1 (102) (Version 5.0) | Topic 108: Essential System Services time, which is implemented by the Network Time Protocol (NTP). In the vast majority of cases, the only configuration a normal user will be required to do is to set their time zone and NTP will take care of the rest. However, we will cover some ways of working with time manually and the specifics of configuring network time will be covered in the next lesson. Local Versus Universal Time The system clock is set to Coordinated Universal Time (UTC), which is the local time at Greenwich, United Kingdom. Usually a user wants to know their local time. Local time is calculated by taking UTC time and applying an offset based on time zone and Daylight Savings. In this way, a lot of complexity can be avoided. The system clock can be set to either UTC time or local time, but it is recommended that it also be set to UTC time. Date date is a core utility which simply prints local time: $ date Sun Nov 17 12:55:06 EST 2019 Modifying the options of the date command will change the format of the output. For example, a user can use date -u to view the current UTC time. $ date -u Sun Nov 17 18:02:51 UTC 2019 Some other commonly-used options will return the local time in a format which adheres to an accepted RFC format: -I Date/time in ISO 8601 format. Appending date (-Idate) will limit the output to date only. Other formats are hours, minutes, seconds and ns for nanoseconds. -R Returns date and time in RFC 5322 format. 248 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 108.1 Maintain system time --rfc-3339 Returns date and time in RFC 3339 format. The format of date can be customized by the user with sequences specified in the man page. For example, the current time can be formatted as Unix time thusly: $ date +%s 1574014515 From date 's man page we can see that %s refers to Unix time. Unix time is used internally on most Unix-like systems. It stores UTC time as the number of seconds since Epoch, which has been defined as January 1st, 1970. The number of bits required to store Unix time at the present moment is 32 bits. There is a future issue when 32 bits will become insufficient to contain the current NOTE time in Unix format. This will cause serious issues for any 32-bit Linux systems. Fortunately, this will not occur until January 19, 2038. Using these sequences, we are able to format date and time in almost any format required by any application. Of course, in most cases it is far preferable to stick with an accepted standard. Additionally, date --date can be used to format a time that is not the current time. In this scenario, a user can specify the date to be applied to the system using Unix time for example: $ date --date='@1564013011' Wed Jul 24 20:03:31 EDT 2019 Using the --debug option can be very useful for ensuring that a date can be successfully parsed. Observe what happens when passing a valid date to the command: $ date --debug --date="Fri, 03 Jan 2020 14:00:17 -0500" date: parsed day part: Fri (day ordinal=0 number=5) date: parsed date part: (Y-M-D) 2020-01-03 date: parsed time part: 14:00:17 UTC-05 date: input timezone: parsed date/time string (-05) date: using specified time as starting value: '14:00:17' date: warning: day (Fri) ignored when explicit dates are given date: starting date/time: '(Y-M-D) 2020-01-03 14:00:17 TZ=-05' date: '(Y-M-D) 2020-01-03 14:00:17 TZ=-05' = 1578078017 epoch-seconds date: timezone: system default Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 249 LPIC-1 (102) (Version 5.0) | Topic 108: Essential System Services date: final: 1578078017.000000000 (epoch-seconds) date: final: (Y-M-D) 2020-01-03 19:00:17 (UTC) date: final: (Y-M-D) 2020-01-03 14:00:17 (UTC-05) This can be a handy tool when troubleshooting an application that generates a date. Hardware Clock A user may run the hwclock command to view the time as maintained on the real-time clock. This command will require elevated privileges, so we will use sudo to call the command in this case: $ sudo hwclock 2019-11-20 11:31:29.217627-05:00 Using the option --verbose will return more output which might be useful for troubleshooting: $ sudo hwclock --verbose hwclock from util-linux 2.34 System Time: 1578079387.976029 Trying to open: /dev/rtc0 Using the rtc interface to the clock. Assuming hardware clock is kept in UTC time. Waiting for clock tick......got clock tick Time read from Hardware Clock: 2020/01/03 19:23:08 Hw clock time : 2020/01/03 19:23:08 = 1578079388 seconds since 1969 Time since last adjustment is 1578079388 seconds Calculated Hardware Clock drift is 0.000000 seconds 2020-01-03 14:23:07.948436-05:00 Note the Calculated Hardware Clock drift. This output can tell you if system time and hardware time are deviating from one another. timedatectl timedatectl is a command that can be used to check the general status of time and date, including whether or not network time has been synchronised (Network Time Protocol will be covered in the next lesson). By default timedatectl returns information similar to date, but with the addition of the RTC 250 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 108.1 Maintain system time (hardware) time as well as the status of the NTP service: $ timedatectl Local time: Thu 2019-12-05 11:08:05 EST Universal time: Thu 2019-12-05 16:08:05 UTC RTC time: Thu 2019-12-05 16:08:05 Time zone: America/Toronto (EST, -0500) System clock synchronized: yes NTP service: active RTC in local TZ: no Setting Time Using timedatectl If NTP is unavailable, it is recommended to use timedatectl rather than date or hwclock to set time: # timedatectl set-time '2011-11-25 14:00:00' The process is similar to that of date. The user can also set time independent of date using the format HH:MM:SS. Setting Timezone Using timedatectl timedatectl is the preferred way of setting the local time zone on systemd based Linux systems when no GUI exists. timedatectl will list possible time zones and then the time zone can be set using one of these as an argument. First we will list possible timezones: $ timedatectl list-timezones Africa/Abidjan Africa/Accra Africa/Algiers Africa/Bissau Africa/Cairo... The list of possible time zones is long, so the use of the grep command is recommended in this case. Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 251 LPIC-1 (102) (Version 5.0) | Topic 108: Essential System Services Next we can set the timezone using one of the elements of the list that was returned: $ timedatectl set-timezone Africa/Cairo $ timedatectl Local time: Thu 2019-12-05 18:18:10 EET Universal time: Thu 2019-12-05 16:18:10 UTC RTC time: Thu 2019-12-05 16:18:10 Time zone: Africa/Cairo (EET, +0200) System clock synchronized: yes NTP service: active RTC in local TZ: no Keep in mind that the name of the time zone must be exact. Africa/Cairo for example will change the time zone, but cairo or africa/cairo will not. Disabling NTP Using timedatectl In some cases it might be necessary to disable NTP. This could be done using systemctl but we will demonstrate this using timedatectl: # timedatectl set-ntp no $ timedatectl Local time: Thu 2019-12-05 18:19:04 EET Universal time: Thu 2019-12-05 16:19:04 UTC RTC time: Thu 2019-12-05 16:19:04 Time zone: Africa/Cairo (EET, +0200) NTP enabled: no NTP synchronized: no RTC in local TZ: no DST active: n/a Setting Time Zone Without timedatectl Setting time zone information is a standard step when installing Linux on a new machine. If there is a graphical installation process, this will most likely be handled without any further user input. The /usr/share/zoneinfo directory contains information for the different time zones that are possible. In the zoneinfo directory, there are subdirectories that contain the names of continents as well as other symbolic links. It is recommended to find your region’s zoneinfo starting from your continent. 252 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 108.1 Maintain system time zoneinfo files contain rules required to calculate the local time offset in relation to UTC, and they also are important if your region observes Daylight Savings Time. The contents of /etc/localtime will be read when Linux needs to determine the local time zone. In order to set the time zone without the use of a GUI, the user should create a symbolic link for their location from /usr/share/zoneinfo to /etc/localtime. For example: $ ln -s /usr/share/zoneinfo/Canada/Eastern /etc/localtime After setting the correct time zone, it is often recommended to run: # hwclock --systohc This will set the hardware clock from the system clock (that is, the real-time clock will be set to the same time as date). Please note that this command is run with root privileges, in this case by being logged in as root. /etc/timezone is similar to /etc/localtime. It is a data representation of the local time zone, and as such it can be read using cat: $ cat /etc/timezone America/Toronto Note that this file is not used by all Linux distributions. Setting Date and Time Without timedatectl Most modern Linux systems use systemd for its configuration and services and as such it is not recommended that you use date or hwclock for setting time. NOTE systemd uses timedatectl for this. Nonetheless it is important to know these legacy commands in the event that you must administer an older system. Using date date has an option to set the system time. Use --set or -s to set the date and time. You may also choose to use --debug to verify the correct parsing of the command: # date --set="11 Nov 2011 11:11:11" Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 253 LPIC-1 (102) (Version 5.0) | Topic 108: Essential System Services Note that root privileges are required to set the date here. We may also choose to change to time or date independently: # date +%Y%m%d -s "20111125" Here we must specify the sequences so that our string is parsed properly. For example %Y refers to the year, and so the first four digits 2011 will be interpreted as the year 2011. Similarly, %T is the sequence for time, and it is demonstrated here by setting time: # date +%T -s "13:11:00" After changing system time, it is recommended to also set the hardware clock so that both system and hardware clocks are synchronised: # hwclock --systohc systohc means “system clock to hardware clock”. Using hwclock Rather than setting the system clock and updating the hardware clock, you may choose to reverse the process. We will start by setting the hardware clock: # hwclock --set --date "4/12/2019 11:15:19" # hwclock Fri 12 Apr 2019 6:15:19 AM EST -0.562862 seconds Notice that by default hwclock is expecting UTC time, but returns the local time by default. After setting the hardware clock, we will need to update the system clock from it. hctosys can be understood to mean “hardware clock to system clock”. # hwclock --hctosys 254 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 108.1 Maintain system time Guided Exercise 1. Indicate whether the following commands are displaying or modifying system time or hardware time: Command(s) System Hardware Both date -u hwclock --set --date "12:00:00" timedatectl timedatectl | grep RTC hwclock --hctosys date +%T -s "08:00:00" timedatectl set- time 1980-01-10 2. Observe the following output, and then correct the format of the argument so that the command is successful: $ date --debug --date "20/20/12 0:10 -3" date: warning: value 20 has less than 4 digits. Assuming MM/DD/YY[YY] date: parsed date part: (Y-M-D) 0002-20-20 date: parsed time part: 00:10:00 UTC-03 date: input timezone: parsed date/time string (-03) date: using specified time as starting value: '00:10:00' date: error: invalid date/time value: date: user provided time: '(Y-M-D) 0002-20-20 00:10:00 TZ=-03' date: normalized time: '(Y-M-D) 0003-08-20 00:10:00 TZ=-03' date: ---- -- date: possible reasons: date: numeric values overflow; date: incorrect timezone date: invalid date ‘20/20/2 0:10 -3’ Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 255 LPIC-1 (102) (Version 5.0) | Topic 108: Essential System Services 3. Use the date command and sequences so that the system’s month is set to February. Leave the rest of the date and time unchanged. 4. Assuming that the command above was successful, use hwclock to set the hardware clock from the system clock. 5. There is a location called eucla. What continent is it part of? Use the grep command to find out. 6. Set your current timezone to that of eucla. 256 | learning.lpi.org | Licensed under CC BY-NC-ND 4.0. | Version: 2023-07-13 LPIC-1 (102) (Version 5.0) | 108.1 Maintain system time Explorational Exercises 1. Which method of setting time is optimal? In what scenario might the preferred method be impossible? 2. Why do you think there are so many methods to accomplish the same thing, i.e. setting system time? 3. After January 19, 2038, Linux System Time will require a 64-bit number to store. However, it is possible that we could simply choose to set a “New Epoch”. For example, January 1st, 2038 at midnight could be set to a New Epoch Time of 0. Why do you think this has not become the preferred solution? Version: 2023-07-13 | Licensed under CC BY-NC-ND 4.0. | learning.lpi.org | 257 LPIC-1 (102) (Version 5.0) | Topic 108: Essential System Services Summary In this lesson you learned: How to display the time in different formats fr

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