Linux L2 — Commands used by DevOps engineers.

Cloudy Buddy

7 min readNov 23, 2023

Real_Time Linux commands for day-to-day use ( DevOps Engineer )

1, System_Commands →

# ls — list the file/folder in the current directory.
# ls -larth — list files/folders in a current directory in detailed format.
# stat <fileName/dirName> — shows detailed information about the file or directory.
# cal — view calendar.
# hostname — shows the name of the system host.
# hostid — shows the host id of the system assigned by the OS.
# date — shows the current date and time in UTC format.
# whoami — shows the currently logged-in username of the terminal.
# uptime — shows the elapsed time duration since the machine logged in.
# uname — unix name.
# clear — clears the screen.
# history — lists all the commands executed until now.
# sudo -i — Super User Do
# echo $? — shows the exit status of the last executed command (0 — success, 1–255 — error/failure).
# shutdown -r now — restart the machine immediately (-r restart).
# printenv — displays all the environment variables of the Linux system.
# last — shows previous logins in the Linux system.

2, Directory Commands →

# pwd — shows the present working directory (abbr. Print Working Directory).
# cd — change directory.
# cd .. — changes to its parent directory (i.e.) one level up.
# cd <dirName> — change to the directory mentioned.
# cd ~ or cd — changes to the currently logged-in user’s home directory.
# cd ../.. — changes the directory two levels up.
# cd — — changes to the last working directory.
# mkdir <dirName> — creates the directory.
# mkdir -p <pathOftheDir> — creates a directory with its parent directories if it does not exist (-p parent).

3, File Commands →

# touch — creates an empty file or updates the timestamp of the existing file.
# touch <fileName> — creates a single empty file.
# touch <file1> <file2> — creates file1, file2 empty files.
# cat — concatenates and displays the contents of files.
# cat <fileName> — displays the contents of the file.
# cat > <fileName> — creates a new file, allows to input content interactively and redirects inputted content to the created file (> redirection operator).
# head <fileName> — displays first 10 lines of the file by default.
# head -n 5 <fileName> — displays first 5 lines of the file (-n number)
# tail <fileName> — displays the last 10 lines of the file by default.
# tail -n 5 <fileName> — displays last 5 lines of the file (-n number).
tail -F <fileName> — displays contents of the file in real-time even when the file is rotated or replaced (used for log file monitoring).
# less <fileName> — used to view large files (log files) in a paginated manner.

rm — remove commands

# rm <fileName> — removes the file.
# rm -r <dirName> — removes files & folders of directory recursively (-r recursive).
# rm -rf <dirName> — force remove the files & folders of directory recursively (-f force).

cp — copy commands

# cp <source> <destination> — copy the files and folders from source to destination.
cp -r <dir1> <dir2> — copy dir1 directory to dir2 directory recursively (-r recursive).

mv — move or rename commands

mv <fileName> <newFileName> — renames the file to a new name.
mv <oldFilePath> <newFilePath> — moves the file to new path.

4, File Permission Commands →

chmod <octalNumber> <fileName> — changes mode/permissions of the file.
chmod <octalNumber> -R <dirName> — changes mode/permissions of the directory recursively.
chown <newUser> <fileName> — changes the user ownership of a file.
chown <newUser>:<newGroup> <fileName> — changes the user & group ownerships of a file.
chgrp <groupName> <fileName/dirName> — updates the group name for file/directory.
getfacl <fileName/dirName> — shows the file/directory access control list.
setfacl -m u:<userName>:rwx <fileName/dirName> — modifies the current acl of the file/directory.
setfacl -x u:<userName>: <fileName/dirName> — removes the acl permissions for the file/directory.
setfacl -m g:<groupName>:rwx <fileName/dirName> — modifies the group acls for the file/directory.
setfacl -x g:<groupName>: <fileName/dirName> — removes the group acl permissions for the file/directory.
File Permission Octal Numbers

read (r) — 4, write (w)- 2, execute (x) — 1 => chmod 777 < file /folder_name >

5, User Management Commands →

useradd — creates a user account.
useradd <userName> — creates user account without home & mail spool directories.
useradd -m <userName> — creates user account with home & mail spool directories.
passwd <userName> — creates a password for the user and stores it in /etc/shadow file.
userdel — user delete.
userdel <userName> — deletes the user from the system.
userdel -r <userName> — deletes the user from the system along with home and mail spool directories (-r remove).
/etc/passwd — stores information about user accounts.
cat /etc/passwd — displays the complete list of users on that machine.
/etc/shadow — stores the password for users in an encrypted format.
cat /etc/shadow — displays the complete list of user passwords on that machine.
su — substitute user.
su <userName> — switches to the user mentioned.
exit — to log out from that user.
usermod — modify user.
usermod -aG <groupName> <userName> — adds the user to another group (-aG append the user to the group without removing from other groups).
chsh — change shell.
chsh -s /bin/bash <user> — changes the shell to bash for the user.
chsh -s /bin/sh <user> — changes the shell to sh for the user.

6, Group Management Commands →

groupadd <groupName> — creates the group.
groupdel <groupName> — delete the group.
/etc/group — stores the information of the groups.
cat /etc/group — displays the complete list of groups on that machine.
gpasswd <groupName> — creates a password for the group.
gpasswd -a <userName> <groupName> — adds the user to the group.
gpasswd -d <userName> <groupName> — removes the user from the group.
gpasswd -M <userName1>,<userName2>,<userName3> <groupName> — adds multiple users to the group and removes the existing ones of the group.

7, Searching Commands →

locate — used to search for files/directories based on names.
sudo updatedb — updates the database so the results are up-to-date.
locate <fileName/dirName> — locates the file/directory and displays the path.

GREP Command s— Global Regular Expression Print →

grep <textToSearch> <fileName> — used to find text patterns within files.
grep -i <textToSearch> <fileName> — used to find text patterns within the file ignoring the case (-i ignore case).
grep -v <textToSearch> <fileName> — used to find non matching lines of text patterns (-v invert-match).
grep -l <textToSearch> <fileNames> — used to display the matching string file names.

Find Commands →

# find. -name <fileName> — finds the mentioned file if available in the current directory (.(period) represents current directory).
# find <dirName> -name <fileName> — finds the mentioned file in the directory.
# find <dirName> -perm 754 — finds the files in the directory having 754 permission.

8, Hardware Commands →

# free -h — shows systems memory information ( -h human-readable format).
# df -h — shows the disk space usage of mounted file systems.
# du — disk usage.
# du -h — displays disk usage information (-h human-readable format).
# du -sh — displays the total size of the directory instead of individual files in human-readable format (-s summarize).
# du -sh <fileName/dirName> — displays the total size of the file/directory.

9, Network Commands →

# ping <hostName> — tests the reachability & responsiveness of the remote host.
# dig <domainName> — shows DNS information of the domain.
# wget <url>- used to retrieve/download files from the internet.
# curl — client URL.
# curl <url> — used to retrieve/download files from the internet.
# ifconfig — display available network interfaces.
# ip addr — display and manipulate network interface info.
# curl ifconfig.me — shows the public IP address of the machine.
# netstat -antp- shows all TCP open ports (-a all, t-tcp, n-active, p protocol).
# traceroute <url> — traces the route using packets from source to destination host.

10, Process Info Commands →

# ps — process status.
# ps — shows the currently running process.
# ps -u <userName>- shows the process of the username
# ps -ef — shows all the processes of the system.
# top — shows the real-time, dynamic view of the running processes of a system.
# kill <pid> — gracefully terminates the process pid.
# pgrep <processName> — shows process ID of processes based on name/other criteria.
# bg — background, sends the process to the background & continues execution without interruption.
# fg — foreground, brings the process to the foreground and makes it an active process.
# nohup — no hangup, runs command/script in the background even after the terminal is closed or the user logs out.

11, Archiving File Commands →

# tar — tape archive.
# tar -cvf <fileName> <directory> — creates the tar file with the fileName for the directory mentioned (-c create, -v verbose, -f output file name).
# tar -xvf <sourceTarFileName> -C <destinationDir> — puts the extracted files into the destination directory (-x extract, -v verbose, -f source tar file name, -C change the folder and download to destination dir).

Package Manager — LINUX DISTROS →

apt — Package Manager for Debian-based Linux distributions Eg: Ubuntu.
yum — Package Manager for Redhat-based Linux distributions Eg: Amazon_Linux.