Essential Linux Command Cheat Sheet for System Administrators

Basic Commands

uname -m

– display processor architecture uname -r – display kernel version dmidecode -q – show hardware components cat /proc/cpuinfo – view CPU details cat /proc/meminfo – view memory usage cat /proc/interrupts – view interrupts lspci -tv – list PCI devices lsusb -tv – list USB devices date – show system date cal 2007 – display calendar for 2007

Shutdown and Reboot

shutdown -h now

– immediate shutdown init 0 – shutdown (runlevel 0) telinit 0 – shutdown (telinit) shutdown -h HH:MM & – schedule shutdown shutdown -c – cancel scheduled shutdown shutdown -r now – immediate reboot reboot – reboot logout – logout

File and Directory Operations

cd /home

– change to /home cd .. – go up one level pwd – print working directory ls – list files ls -l – detailed list ls -a – include hidden files tree – tree view of directories mkdir dir1 – create directory mkdir -p /tmp/dir1/dir2 – create nested directories rm -f file1 – force delete file rmdir dir1 – remove empty directory rm -rf dir1 – recursively delete directory mv dir1 new_dir – rename or move cp file1 file2 – copy file ln -s file1 link1 – create symbolic link ln file1 link1 – create hard link

File Search

find / -name file1

– search from root find /home/user1 -name \*.bin – search for *.bin locate \*.ps – fast locate (run updatedb first) whereis halt – locate binary/source/man which halt – show executable path

Mounting Filesystems

mount /dev/hda2 /mnt/hda2

– mount device umount /dev/hda2 – unmount device mount -o loop file.iso /mnt/iso – mount ISO image mount -t vfat /dev/hda5 /mnt/hda5 – mount FAT32

mount -t smbfs -o username=user,password=pass //WinClient/share /mnt/share

– mount Windows share

Disk Space Utilities

df -h

– show mounted partitions du -sh dir1 – estimate directory size rpm -qa | sort -k1,1n – list installed RPMs by size (Fedora/RedHat) dpkg-query -W | sort -k1,1n – list installed DEBs by size (Debian/Ubuntu)

User and Group Management

groupadd group_name

– create group useradd -c "Name" -g admin -d /home/user1 -s /bin/bash user1 – create user with details passwd user1 – change password usermod -g system -d /ftp/user1 -s /bin/nologin user1 – modify user groupdel group_name – delete group userdel -r user1 – delete user and home

File Permissions

chmod ugo+rwx directory1

– grant rwx to all chmod go-rwx directory1 – revoke from group/others chown user1 file1 – change owner chgrp group1 file1 – change group chmod u+s /bin/file1 – set SUID chmod g+s /home/public – set SGID on directory chmod o+t /home/public – set sticky bit

Special File Attributes

chattr +i file1

– make immutable chattr +a file1 – append‑only chattr +c file1 – enable compression lsattr – list attributes

Package Management (RPM, YUM, DEB, APT)

rpm -ivh package.rpm

– install RPM rpm -e package_name – erase RPM yum install package_name – install via YUM yum update package_name – update package dpkg -i package.deb – install DEB apt-get install package_name – install via APT

Backup and Synchronization

dump -0aj -f /tmp/home0.bak /home

– full backup restore -if /tmp/home0.bak – restore backup rsync -az -e ssh /home user@host:/tmp – sync over SSH dd if=/dev/sda of=/tmp/file1 – raw disk copy tar -cvf backup.tar /home/user – archive directory

Network Utilities

ifconfig eth0

– show interface config route -n – display routing table netstat -tup – list active connections tcpdump tcp port 80 – capture HTTP traffic ping www.example.com – test connectivity nslookup www.example.com – DNS lookup

Directory Listing and File Type

ls -a

– show all files ls -l – detailed list ls -R – recursive list file file1 – determine file type

Text Processing

grep pattern file

– search text sed 's/old/new/g' file – stream edit awk '{print $1}' file – field extraction sort file | uniq – unique sorted lines tr '[:lower:]' '[:upper:]' – case conversion

Character Conversion and File Format

dos2unix filedos.txt fileunix.txt

– DOS to UNIX unix2dos fileunix.txt filedos.txt – UNIX to DOS recode ..HTML < page.txt > page.html – convert to HTML

Filesystem Checks and Initialization

fsck /dev/hda1

– check/repair filesystem mkfs /dev/hda1 – create filesystem mke2fs -j /dev/hda1 – create ext3 with journaling badblocks -v /dev/hda1 – scan for bad blocks

Swap Management

mkswap /dev/hda3

– create swap area swapon /dev/hda3 – enable swap

VIM Editor Basics

vim file

– open file in VIM :q – quit i – insert mode Esc – return to command mode dd – delete line yy – yank (copy) line p – paste :wq – write and quit

Additional Utilities

tar -cvzf archive.tar.gz dir

– create compressed tarball gzip file – compress file unzip file.zip – extract zip dd if=/dev/hdc | md5sum – compute MD5 of device who – list logged‑in users dmesg – kernel ring buffer free -h – memory usage