Linux Commands

• The uname command displays information about the Linux kernel.

Commands

• Valid command lines include Is -l /etc and Is /etc -l
• To delete a variable, use the unset command.
• To view all processes, execute ps -e.
• To run a command in the background, type <command>&
• Use killall to send a signal to a set of processes with the same name
• echo ???a command displays only a file named ???a
• The bash command performs globbing

rm Command

• The -R and -r options for the rm command can be used to delete directories that contain files

Utilities

• gzip and bzip are not aliases for the same utility
• bzip2 does not support recursive compression

dd Command

• The dd command can create large files that can be used as swap files
• The dd command can copy entire partitions
• stdout is the output stream of a command operating normally
• Two or more commands combined with the | between them form a pipeline
• Use 2>> to append a file with the normal output of a command
• Use &> to send the normal and error output of a command to a single file

File Manipulation

• The paste command merges two files together line by line
• sed is a non-interactive editor
• Use the nl command to display a file with its lines numbered
• The sort command puts the lines of a file in alphabetical order
• The pr command provides formatting options for printing a file

Regular Expressions

• The . Matches any one character in regular expressions
• The * Matches zero or more of the previous character in regular expressions
• The regular expression a? is equivalent to a{0,1}
• To use regular expression characters to match themselves, do not use the slash in front of the character

vi Command Mode Navigation

• Press $ to navigate to the end of the line in vi command mode
• Press b to move backward through a vi document, word by word
• To save and then quit in vi command mode, type :wq
• Press h or the left arrow key to move a character to the left in vi command mode
• Press k or the up arrow key to move up a line in vi command mode

File Permissions

• An octal permission mode of 750 corresponds to rwxr-x---
• Only root can change the owner of a file
• With rw-r--x permissions, both the user owner and group owners can view the contents of a file, assuming everyone has access to the directory the file is in
• To switch to another group, you must be a member of the group you are switching to
• chmod 0777 /data will remove all special permissions

Disk Quotas

• userquota and grpquota are mount options used for disk quotas
• The repquota command lists the users of groups and their quota statistics
• mount -o remount /data will remount the /data filesystem using the option from the /etc/fstab file
• If a user has exceeded the block soft quota and the grace period has expired, the soft limit becomes a hard limit until the user goes below the soft limit again

Directories with Writable Permissions

• The /tmp and /var/tmp directories are typically writable to all users
• Execute swapon to activate an initialized swap space

Partition Management

• Use sfdisk to backup a partition table to a file and restore it later
• Use vgextend to add a physical volume to an existing volume group
• Use Isof and fuser to check what is keeping the partition busy
• mount and df commands can display a list of mounted file systems
• The first field in /etc/fstab specifies the device to mount
• The sixth field in the /etc/fstab file is used to specify fsck order
• mount -o loop cdrom.iso /mnt will mount an ISO file named cdrom.iso
• The -S du command option shows a summary of the space used in a directory structure.
• The number of inodes determines how many files can be stored in a filesystem.
• tune2fs and dumpe2fs commands will display information about the Superblock
• The fsck utility uses the /etc/fstab file to determine a filesystem type
• dumpe2fs command will allow determining where the backup superblock is for a filesystem
• The output of ls -l command includes the file /etc/grub.conf as the soft link file

Hard vs Soft Links

• If you have 5 hard linked files and you delete four of them, the data is still available from the remaining file
• The /mnt directory is used as a temporary mount point
• Use the lilo command needs to be executed after modifying the LILO configuration file
• The boot is a directive is not typically used after a title directive in GRUB Legacy
• The kernel phase is the third stage of the boot process
• The bootloader loads the ramdisk into memory
• The kernel is a component of memory
• Runlevel 2 is used to define multi-user with no networking services

System Commands

• The commands reboot and shutdown -r can be used to reboot the Linux system
• The uname -s option to will display the kernel name

RPM Packages

• An RPM command requires the full filename when querying the package
• The package file requires the -p option to query
• When using the -f option when performing an rpm query, the command will show the package that owns a file
• rpm -U figlet-1.1-0.3.i686.rpm and rpm -i figlet-1.1-0.3.i686.rpm commands will install a RPM package file

Other Commands

• The rpm2cpio command can extract files from a -.rpm file and list the content of a -.rpm file
• The automatically searched directories for shared libraries are /usr/lib and /lib
• The command apt-get purge will remove all files that belong to a Debian package
• apt-get update command will update the list of available packages for APT
• The dpkg -S command determines the Debian package that owns a file
• dpkg –I can be used get a list of the installed Debian packages
• The apt-cache show and dpkg -s commands will show detailed information about a Debian package

Linux Executables

• Idd command is used to display the shared libraries of a dynamically linked executable
• rpm -qKp command will check the integrity of an RPM file
• The 1 special file man pages are typically located in section for Shell commands
• The / character always starts with an absolute path
• Place ~/.bash_logout in your home directory to be executed when you log off the system
• The ps command lists the commands that are running in your terminal
• You must log in as the root user in order to set a priority value lower than 0
• Character ? exactly matches one character in glob
• The touch command's default action on an existing file will update the file's timestamp

find Command

• The -exec option will execute a command on each matching file without prompting in find command
• The -iname option find command will search by name using a case-insensitive match
• The command Is > /tmp/output.txt takes the standard output of Is and puts it into the /tmp/output.txt file
• The -p option is used with the edquota command to copy the quota limits from one user account to another.
• A dual boot system contains both Linux and a Microsoft Windows operating system
• Most users home directories are found in /home.
• Virtual memory is also referred to as swap memory.
• The /var structure has directories which may have heavy activity for services like mail, ftp, httpd and printing

Additional Information

• After running fdisk -cu /dev/sdb, the w fdisk command allows you to save changes and quit
• Ivcreate is used to create a logical volume
• The -m option to the tune2fs command changes the space reserved for system use
• The -exclude option with the du command allows specifying a subdirectory to not include in the results
• -f is the option to the fsck command forces a system check
• The -t fsck command option specifies the filesystem type
• The -b indicates soft link in the Is -I command
• Soft links can be made to directories
• Soft links can only be made to a file on another filesystem
• The /boot directory stores the kernel
• Full path to the LILO configuration file is /etc/lilo.conf

Encrypted Passwords

• To use an encrypted password in the GRUB Legacy configuration file, use the -crypt option for the password directive
• Primary configuration file for the GRUB 2 on a Fedora system is /boot/grub2/grub.cfg
• The first process that the kernel launches is called the init process
• The program that first starts the boot process is called the bootloader
• Shared libraries make Programs smaller and use a more consistent base of code
• The include Id.so.conf.d/*.conf contents are in the Idconfig configuration file by default
• The libraries used by the /bin/Is command are displayed using Idd /bin/ls
• It's false that the same set of services are started or stopped at different runlevels
• The default runlevel for Debian based Linux systems is 2
• bootup is not a Linux boot system
• The /var/log/dmesg file is overwritten at the end of each boot process with the messages that were generated while booting
• Use the command free to view the summary of the RAM and swap space
• True, Coldplug devices are devices that are connected when the power is off
• Ispci to view the network interface controller connected on the PCI bus
• HALD is the abbreviation and stands for Hardware Abstraction Layer Daemon
• HALD uses dbus to send notifications about any changes in the state of hardware devices