Basic Linux Commands

These examples apply to common Linux tools, with current equivalents for Rocky Linux 9. Replace placeholder names such as filename, PID, and username with your own values. Commands requiring sudo are for authorized administrators, not routine cluster work. Optional tools may need to be installed.

Rocky Linux 9: Useful Commands

cat /etc/os-release
ip -brief address
ip route show
ss -tuna
systemctl status SERVICE_NAME
journalctl -u SERVICE_NAME
python3 --version
dnf info PACKAGE_NAME

Use man COMMAND for the version installed on your machine. Administrators can install a package with sudo dnf install PACKAGE_NAME. Use qdel JOB_ID for a scheduled cluster job rather than attempting to terminate it with kill or killall.

Basic Commands
cat filename.txt	Print the contents of filename.txt to your screen
cd -	Change to the last visited directory
cd ..	Move up one directory level.
cd dirname	Change into directory "dirname"
cd ~ or cd	Change into your home directory
chmod	Change file access permissions: USER, GROUP, and OTHERS. 0 = --- No permission 1 = --x Execute only 2 = -w- Write only 3 = -wx Write and execute 4 = r-- Read only 5 = r-x Read and execute 6 = rw- Read and write 7 = rwx Read, write and execute
`chmod 000 filename`	Remove all owner, group, and other permission bits. This does not prevent privileged access, and the owner can normally restore permissions.
`chmod 644 filename`	Allow the owner to read and write; allow the group and others to read.
`chmod 755 filename`	Allow the owner to read, write, and execute; allow the group and others to read and execute.
chown root myfile.txt	Changes the owner of the file to root [requires root privileges].
chown owner:group myfile.txt	Change the file's owner and group to the specified owner and group [requires root privileges].
`cp -a source/. destination/`	Copy a directory’s contents, including hidden files, while preserving attributes where permitted. The destination should be a directory.
`cp -av . /path/to/newdirectory`	Copy the current directory, including hidden files, recursively and print the copied names. Use a destination outside the source tree.
cp filename filename.bak	Copies filename to filename.bak
`file *`	Identify the type of each non-hidden pathname matched by the shell’s * pattern.
`file filename`	Identify the file type using its contents and metadata.
find / -name "filename"	Finds the file called "filename" on your filesystem starting the search from the root directory "/".
find	Utility to find files / directories on a computer.
grep	Looks for patterns in file(s)
`grep word filename.txt`	Print lines containing a match for the pattern word. Use grep -w word filename.txt to match a whole word.
`grep -v word filename.txt`	Print lines that do not match the pattern word.
gv	View PostScript/PDF files.
less	Similar to the more command.
`ln -s /home/user/file1 /home/user/file2`	Create file2 as a symbolic link to file1. Editing file2 normally changes file1; removing the link does not remove file1.
`ln target link_name`	Create a hard link to a file. Use ln -s target link_name for a symbolic link, including links to directories.
`locate filename`	Search an indexed filename database. Results may be outdated; the locate package and database may not be installed. Use find for a live search.
ls -la	Show files and directories, including hidden entries, with detailed attributes.
ls	List files in the current directory.
more filename	Display the contents of "filename" one screen at a time. Press the space bar to advance to the next page, or q to quit.
mv	Move or rename a file.
mv oldfilename newfilename	Move a file or directory from oldfilename to newfilename
nl	Number lines
od	View binary files and data
rm -f filename.txt	Delete filename.txt without asking for confirmation.
rm -rf tmp/	Recursively delete the tmp directory and its contents, including subdirectories.
rm	Deletes a file
rm -i filename.txt	Ask for confirmation before deleting the file.
stat	Display file attributes
`tail -n 100 filename`	Print the last 100 lines of filename.
tail -f filename	Monitor the file continuously as it is updated.
`tail filename`	Print the last 10 lines by default.
`touch filename`	Update access and modification times. Create an empty file if it does not exist; do not erase existing contents.
`touch /home/user/filename.txt`	Create this file if absent, or update its timestamps if it already exists.
wc -l filename.txt	Count the lines in filename.txt.
`wc filename`	Print newline, word, and byte counts. Use -l for newline counts, -w for words, -c for bytes, or -m for characters.
xdvi	View TeX DVI files
xxd	Also view binary files and data
Editors
pico, vi, emacs	The most popular editors
vi filename.txt	Edit filename.txt. Press Esc to enter Normal mode before issuing editing commands. Use i to enter Insert mode. Commands are case-sensitive; see the examples below. H --- Upper left corner (home) M --- Middle line L --- Lower left corner h --- Back a character j --- Down a line k --- Up a line ^ --- Beginning of line $ --- End of line l --- Forward a character w --- Forward one word b --- Back one word fc --- Find c ; --- Repeat find (find next c) :q! --- This force quits the file without saving and exits vi :w --- This writes the file to disk, saves it :wq --- Save the file to disk and exit vi. :$ --- Takes you to the last line of the file :0 --- Takes you to the first line of the file See the quick reference guide in txt format.
emacs -nw filename.txt	C-h t --- Open the Emacs tutorial. C-x C-c exit emacs C-x C-f --- read a file into emacs C-x C-s --- save a file back to disk C-f --- move forward one character C-b --- move backward one character C-n --- move to next line C-p --- move to previous line C-a --- move to beginning of line C-e --- move to end of line M-f --- move forward one word M-b --- move backward one word C-v --- move forward one screen M-v --- move backward one screen M-< --- go to beginning of file M-> --- go to end of file See the quick reference guide in txt format or pdf format.
Network commands
`ip neigh`	Display the neighbor table, including IPv4 ARP entries. This is the current alternative to arp.
`ip address show`	Display addresses and state for all network interfaces.
`ip -brief address`	Display a concise list of interfaces, their state, and their addresses.
`ss -a -n`	Display listening and non-listening sockets using numeric addresses and ports.
`ss -Htn state established '( sport = :80 )' \| wc -l`	Count established TCP connections with local port 80. This is a connection count, not a count of users or requests.
`ip route show`	Display IPv4 routes. Use ip -6 route show for IPv6.
`ss -tuna`	Display TCP and UDP sockets, including listening sockets, using numeric addresses and ports.
nslookup beowulf.rutgers.edu	Query the default Domain Name System (DNS) server for a host's name or IP address.
ping beowulf.rutgers.edu	Sends test packets to a specified server (beowulf.rutgers.edu in this example) to check if it is responding properly
`ip route show`	Display the IPv4 routing table.
`sudo tcpdump -i INTERFACE`	Capture packets on the selected interface. Replace INTERFACE with an actual interface name. Capture requires suitable privileges and may expose sensitive traffic.
top -u root	Show only processes running as root.
top	Shows live system processes in a formatted table, memory information, uptime and other useful info. While in top, Shift + M to sort by memory usage or Shift + P to sort by CPU usage
traceroute beowulf.rutgers.edu	Show the route your packets take to the destination host.
w	Shows who is currently logged in and where they are logged in from.
`who`	Display logged-in users, terminals, and login times.
System commands
`date`	Display the current date and time. Changing system time requires privileges; administrators normally use timedatectl on Rocky Linux 9.
`dmesg \| less`	View kernel messages. Access may require sudo, depending on the system configuration.
du -sh	Shows a summary of total disk space used in the current directory, including subdirectories.
`du -h dirname \| less`	Display disk space used by dirname and its subdirectories. For apparent file sizes, add --apparent-size.
du	Shows disk usage.
`free -h`	Display memory and swap usage in readable units. Without -h, the default unit is KiB.
`fsck`	Check or repair a supported file system. This is an administrator task; do not run repairs on a mounted file system. XFS uses different tools.
`hostname`	Display the hostname. Administrators can use hostnamectl to inspect or change the system hostname on Rocky Linux 9.
`kill -KILL PID`	Force termination without allowing cleanup. Try kill PID first. Use only for a process you are authorized to terminate.
`kill PID`	Send SIGTERM by default, allowing the process to handle the signal and clean up. You can normally signal your own processes.
`killall program_name`	Send SIGTERM to processes with this name that you have permission to signal. Replace program_name with the intended executable name.
last -10 -a	Show the last 10 logins, with the hostname in the last field.
last -10	Shows only the last 10 logins.
last	Shows who logged in and when.
`lsmod`	List loaded kernel modules. Listing normally does not require root privileges.
man	topic — Display the system manual pages for the specified topic. Run 'man netstat' for details about the netstat command, including its options and examples.
mount -t auto /dev/cdrom /mnt/cdrom	Mount the CD. The directory /mnt/cdrom must exist [often requires root privileges].
mount -t auto /dev/fd0 /mnt/floppy	Mount the floppy. The directory /mnt/floppy must exist [often requires root privileges].
`mount`	With no arguments, list mounted file systems. Mounting a device requires additional arguments and usually administrator privileges.
`ps -u username`	List processes whose effective user is username.
ps auxf	Show all system processes, organized in a hierarchy.
ps aux	Shows all system processes.
`ps`	Display a snapshot of processes belonging to your effective user and terminal by default. Use ps aux for all processes.
pwd	Display the path of the current working directory.
reboot	Reboot the machine [requires root privileges].
`sudo command`	Run a command as another user, root by default, if your sudo policy permits it. Cluster users should request administrator help for system changes.
time	Determine the amount of time that it takes for a process to complete.
uname -a	Display information about the server, such as the kernel version.
uptime	Show how long the server has been running and its load averages.
`whoami`	Print the effective username, which may differ from the original login name after sudo or su.
Compression commands
bzip2	Compress files in bzip2 format
compress	Compress files. Compressed filenames end in .Z.
`gzip filename`	Compress filename to filename.gz, normally replacing the original. Add -k to keep the original.
`gzip -d filename.gz`	Decompress filename.gz, normally replacing the compressed file. Add -k to keep it.
tar -cf archive.tar dirname	Takes everything from directory dirname and puts it into archive.tar
tar -xvf file.tar	Extracts the files
tar -zxvf file.tar.gz	Extract files from a compressed archive.
`tar`	Archive or extract files; tar alone does not imply compression. Use -z for gzip compression.
uncompress	Decompress files. For example: uncompress filename.Z.
unzip file.zip	Extract files from a .zip archive.
zip	Compress files into a .zip archive.
rpm2cpio pack.rpm \|cpio -ivd	Extract the contents of the RPM package named pack. [cpio command : -i -- extract, -d -- make local subdirectories, -v -- verbose]
rpm2cpio pack.rpm \|cpio -t	List all files in the `pack` package
rpm -qa	To list all RPM packages installed.
`sudo rpm -e PACKAGE_NAME`	Remove an installed RPM package. On Rocky Linux 9, sudo dnf remove PACKAGE_NAME also handles dependency resolution.
`sudo rpm -Uvh package.rpm`	Install or upgrade a local RPM file. Prefer sudo dnf install ./package.rpm when dependencies need to be resolved.
Hidden Configuration Files
.bash_history	The list of executed commands.
.bash_login	Treated by bash like .bash_profile if that doesn't exist.
.bash_logout	Sourced by bash login shells at exit.
.bash_profile	Sourced by bash login shells after /etc/profile
.emacs	Read by emacs at startup
.profile	Treated by bash like ~/.bash_profile if that and .bash_login don't exist.
`.vimrc`	User configuration file for Vim; not a universal configuration file for every vi implementation.
Configuration files
`/etc`	System configuration directory.
/etc/cron*	Directories in this set contain files that define how the crond utility runs applications on a daily (cron.daily), hourly (cron.hourly), monthly (cron.monthly), or weekly (cron.weekly) schedule.
/etc/crontab examples	These are five-field user crontab examples, edited with `crontab -e`. Entries in /etc/crontab and /etc/cron.d files additionally require a username before the command. Minute (0-59) Hour (0-23) Day of month (1-31) Month (1-12 or Jan-Dec) Day of week (0-7; 0 and 7 are Sunday) Command 30 2 12 * 0,6 command At 2:30 a.m. on the 12th of every month and every Saturday and Sunday. When both day fields are restricted, cron matches either field. 0 0,12 1 /2 command At midnight and noon on the 1st of January, March, May, July, September, and November. 0 2 1-10 * * command At 2 a.m. on the 1st through the 10th of each month. 30 12 * * 1,3,5 command At 12:30 p.m. every Monday, Wednesday, and Friday.
/etc/cups	Contains files used to configure the CUPS printing service.
`/etc/default`	Default settings for some programs. The files present depend on the distribution and installed packages.
`/etc/init.d`	Legacy System V service scripts. Rocky Linux 9 primarily uses systemd units and systemctl.
`/etc/mail`	Configuration for mail software that uses this directory; contents depend on installed packages.
`/etc/passwd`	User account records such as usernames, user IDs, home directories, and login shells. On Rocky Linux 9, password hashes are normally stored in /etc/shadow.
/etc/security	Contains files that set a variety of default security conditions for your computer.
`/etc/shadow`	Restricted account password-hash and password-aging information. Passwords are hashed, not stored as reversibly encrypted text.
/etc/skel	Any files contained in this directory are automatically copied to a user’s home directory when that user is added to the system.
`/etc/sysconfig`	Configuration used by some system services. Rocky Linux 9 also uses NetworkManager profiles and systemd configuration; not all service settings are here.
`/etc/rsyslog.conf and /etc/rsyslog.d/`	Rsyslog configuration, when rsyslog is installed. Use journalctl to inspect the systemd journal.
`/etc/xinetd.d`	Legacy configuration for xinetd, if installed. Modern installations may use systemd socket units instead.
/var	Contains variable data like system logging files, mail and printer spool directories, and transient and temporary files.
`/var/log`	Logs from the system and applications. Use journalctl for the systemd journal; individual log files depend on installed services.
`/var/log/messages`	General system messages when rsyslog is configured to write this file. Also check journalctl.
`/run/utmp`	Binary records of current login sessions. Read them with who or w rather than a text editor.
`/var/log/wtmp`	Binary login/logout history, when recorded. Read it with last.

References

GNU Coreutils · GNU grep · Cron format · ip · ss · ps

Basic Linux Commands

Rocky Linux 9: Useful Commands

Basic Commands

Editors

Network commands

System commands

Compression commands

Hidden Configuration Files

Configuration files

References