150 Essential Linux Commands Every Sysadmin Should Master

Online Query and Help Commands

man : Full name manual, used to view various reference manuals built into the system.

help : Displays help information for shell internal commands.

File and Directory Operations

ls : List directory contents and their attribute information.

cd : Change the current working directory to the specified path; "~" denotes the home directory, "." the current directory, and ".." the parent directory.

cp : Copy files or directories.

find : Search for files within a specified directory hierarchy.

mkdir : Create directories.

mv : Move or rename files.

pwd : Print the absolute path of the current working directory.

rename : Batch rename files using string replacement.

rm : Remove one or more files or directories (use with caution).

rmdir : Remove empty directories.

touch : Change file timestamps or create a new empty file if it does not exist.

tree : Display directory contents in a tree-like diagram.

basename : Show the filename, stripping directory path and suffix.

dirname : Show the directory portion of a given path.

chattr : Change file attributes.

lsattr : List file attributes.

file : Identify file types.

md5sum : Generate and verify MD5 checksums for file integrity.

File Viewing and Content Processing Commands

cat : Concatenate and display file contents.

tac : Reverse the order of file lines (last line first).

more : Paginated display of file contents with basic navigation and search.

less : Flexible file viewer allowing forward and backward navigation without preloading the entire file.

head : Show the beginning of a file (default first 10 lines).

tail : Show the end of a file; "-f" follows a file as it grows.

cut : Split each line of a file by a delimiter and output selected fields.

split : Divide a file into smaller pieces.

paste : Merge lines of files column-wise.

sort : Sort text file contents line by line.

uniq : Remove duplicate lines from a sorted file.

wc : Count lines, words, or bytes in a file.

iconv : Convert file encoding.

dos2unix : Convert Windows line endings (\r\n) to Unix/Linux line endings (\n).

diff : Compare files line by line.

vimdiff : Visual file comparison tool using Vim.

rev : Reverse each line character-wise.

grep/egrep : Search text using patterns or regular expressions.

join : Join lines of two files on a common field.

tr : Translate or delete characters from input.

vi/vim : Standard text editors on Unix/Linux, with Vim offering advanced features for programming.

File Compression and Extraction Commands

tar : Create and extract archive files.

unzip : Extract ZIP archives.

gzip : Compress files, adding a ".gz" extension.

zip : Create ZIP archives.

System Information Commands

uname : Display system information.

hostname : Show or set the system's host name.

dmesg : Display kernel boot messages and diagnose system issues.

uptime : Show system uptime and load.

stat : Display file and filesystem status.

du : Show disk usage of files or directories.

df : Report filesystem disk space usage.

top : Real-time system monitor showing process resource usage.

free : Display memory and swap usage.

date : Show or set the system date and time.

cal : Display a calendar.

File Search Commands

which : Locate a command in the directories listed in $PATH.

find : Search for files or directories in the filesystem.

whereis : Locate source, binary, and manual files for a command.

locate : Find files using a prebuilt database (faster than find).

User Management Commands

useradd : Create a new user account.

usermod : Modify existing user attributes.

userdel : Delete a user account.

groupadd : Create a new user group.

passwd : Change a user's password.

chage : Modify password expiration information.

id : Show user and group IDs.

su : Switch to another user account.

visudo : Safely edit the sudoers file.

sudo : Execute commands with elevated privileges.

Basic Network Operations

telnet : Remote login using the TELNET protocol.

ssh : Secure remote login using SSH.

scp : Securely copy files between hosts over SSH.

wget : Download files from a URL.

ping : Test network connectivity between hosts.

route : Display and modify the routing table.

ifconfig : Configure network interfaces (requires root).

ifup : Bring a network interface up.

ifdown : Bring a network interface down.

netstat : Show network status and connections.

ss : Display socket statistics, similar to netstat but faster.

Advanced Network Operations

nmap : Network scanner and mapper for security testing.

lsof : List open files, including network connections.

mail : Send and receive email.

mutt : Email management utility.

nslookup : Interactive DNS query tool.

dig : DNS lookup utility for testing name resolution.

host : Simple DNS lookup tool.

traceroute : Trace the path packets take to a host.

tcpdump : Capture and analyze network packets.

Disk and Filesystem Commands

mount : Mount external filesystems.

umount : Unmount filesystems.

fsck : Check and repair inconsistent filesystems.

parted : Partition disks, supporting large (>2 TB) disks with GPT.

mkfs : Create a filesystem on a device.

partprobe : Re-read partition table from the kernel.

e2fsck : Check ext2/ext3/ext4 filesystems.

mkswap : Set up a swap area.

swapon : Enable a swap partition.

swapoff : Disable a swap partition.

sync : Flush filesystem buffers to disk.

resize2fs : Resize ext2/ext3/ext4 filesystems.

System Permissions and Authorization

chmod : Change file permission modes.

chown : Change file owner and group.

chgrp : Change group ownership of a file or directory.

umask : Set or display the default permission mask for new files.

User Login Information Commands

whoami : Show the current effective username.

who : Display currently logged-in users.

w : Show logged-in users and their running processes.

last : Show recent login history.

lastlog : Display the most recent login of all users.

users : List all logged-in users.

finger : Show detailed information about logged-in users.

Built‑in and Miscellaneous Commands

echo : Print variables or strings.

printf : Format and output data.

rpm : Manage RPM packages.

yum : Front‑end package manager for RPM‑based distributions.

watch : Periodically execute a command and display its output.

alias : Define command aliases.

unalias : Remove command aliases.

clear : Clear the terminal screen.

history : Show command history.

eject : Eject removable media.

time : Measure the execution time of a command.

nc : Netcat, a versatile networking utility.

xargs : Build and execute command lines from standard input.

exec : Replace the shell with a specified command.

export : Set or display environment variables.

unset : Remove variables or functions.

type : Show how a command would be interpreted (builtin, file, etc.).

bc : Arbitrary‑precision calculator language.

System Management and Performance Monitoring

chkconfig : Check and configure system services.

vmstat : Report virtual memory statistics.

mpstat : Report per‑processor statistics.

iostat : Report CPU and I/O statistics.

sar : System Activity Reporter for comprehensive performance data.

ipcs : Report inter‑process communication facilities.

ipcrm : Remove IPC objects.

strace : Trace system calls and signals of a process.

ltrace : Trace library calls of a process.

Shutdown, Reboot, Logout and System Info Commands

shutdown : Power off or reboot the system, optionally sending a warning message.

halt : Halt the system.

poweroff : Power off the machine.

logout : Exit the current shell session.

exit : Exit the current shell session.

Ctrl+d : Shortcut to exit the current shell.

Process Management Commands

bg : Resume a suspended background job.

fg : Bring a background job to the foreground.

jobs : List current background jobs.

kill : Terminate a process.

killall : Terminate all processes with a given name.

pkill : Kill processes by name.

crontab : Schedule recurring tasks.

ps : Display a snapshot of current processes.

pstree : Show processes as a tree.

nice / renice : Adjust process scheduling priority.

nohup : Run a command immune to hangups.

pgrep : Search for processes by name.

runlevel : Show the current system runlevel.

init : Change the system runlevel.

service : Manage system services (start, stop, restart, status).