Linux System Administration Commands Reference

System Information

Commands such as arch , uname -m , cat /proc/cpuinfo , lspci -tv , and lsusb -tv display processor architecture, kernel version, CPU details, PCI and USB devices.

Date and Time

Use cal 2007 to show a calendar, date 041217002007.00 to set date/time, and clock -w to write the system clock to BIOS.

Shutdown and Reboot

Shutdown commands include shutdown -h now , init 0 , telinit 0 , scheduled shutdowns with shutdown -h hh:mm , and reboot with shutdown -r now or reboot . Use logout to log out.

File and Directory Operations

Navigate with cd , list with ls , create directories using mkdir , remove files/directories with rm and rmdir , move/rename with mv , copy with cp , and create links using ln -s (soft) or ln (hard). Additional utilities: tree , lstree , touch , file , iconv .

File Search

Search files with find (e.g., find / -name file1 , find /home/user1 -name *.bin ) and locate with locate , whereis , which .

Mounting Filesystems

Mount and unmount devices using mount /dev/hda2 /mnt/hda2 , umount /dev/hda2 , with options for loop devices, ISO images, FAT32, SMB shares, etc.

Disk Space

Check mounted partitions with df -h , list files by size with ls -lSr | more , estimate directory usage with du -sh dir1 , and list package sizes using rpm -q -a --qf '%10{SIZE}t%{NAME}n' or dpkg-query -W -f='${Installed-Size;10}t${Package}n' .

User and Group Management

Create groups with groupadd , delete with groupdel , modify with groupmod . Manage users with useradd , userdel , usermod , change passwords with passwd , set expiration with chage -E , and verify files with pwck , grpck , newgrp .

File Permissions

Modify permissions using chmod ugo+rwx directory1 , remove with chmod go-rwx directory1 , change ownership with chown user1 file1 , and set group ownership with chgrp group1 file1 . Special bits (SUID, SGID, sticky) are handled with chmod u+s , chmod g+s , chmod o+t , etc.

Special File Attributes

Use chattr +i file1 to make a file immutable, chattr +a for append‑only, chattr +c for compression, and lsattr to view attributes.

Compression and Archiving

Compress/decompress with bzip2 , gzip , gunzip , rar , unrar . Create archives using tar -cvf archive.tar file1 , tar -czvf archive.tar.gz dir1 , tar -cjf archive.tar.bz2 dir1 , and extract with tar -xvf . Zip utilities: zip , unzip .

RPM Package Management (Fedora/RedHat)

Install with rpm -ivh package.rpm , update with rpm -U , query with rpm -qa , list files with rpm -ql package , verify with rpm -V package , and import GPG keys with rpm --import .

YUM Package Manager

Install, update, remove packages using yum install , yum update , yum remove , list packages with yum list , search with yum search , and clean caches with yum clean all .

DEB Package Management (Debian/Ubuntu)

Install with dpkg -i package.deb , remove with dpkg -r , list installed packages with dpkg -l , query files with dpkg -L , and locate providing package with dpkg -S /bin/ping .

APT Tools

Manage packages using apt-get install , apt-get update , apt-get upgrade , apt-get remove , and search with apt-cache search .

Viewing File Contents

Use cat , tac , more , less , head , tail , and tail -f for real‑time monitoring.

Text Processing

Combine files with cat , filter with grep , transform with sed (e.g., sed 's/string1/string2/g' ), and process columns with awk , paste , sort , uniq , comm .

Character Conversion

Convert line endings with dos2unix and unix2dos , and recode files using recode .

Filesystem Analysis

Check for bad blocks with badblocks -v /dev/hda1 and repair filesystems with fsck , e2fsck , fsck.ext2 , fsck.ext3 , fsck.vfat , etc.

Filesystem Creation

Create filesystems with mkfs /dev/hda1 , mke2fs -j /dev/hda1 , mkfs -t vfat 32 -F /dev/hda1 , format floppy with fdformat -n /dev/fd0 , and create swap with mkswap /dev/hda3 .

Swap Management

Enable swap using swapon /dev/hda3 and disable with swapoff .

Backup Utilities

Perform backups with dump and restore with restore , synchronize directories with rsync , create disk images with dd , and archive with tar combined with ssh for remote copies.

CD/DVD Operations

Burn discs with cdrecord , create ISO images with mkisofs , mount ISO files with mount -o loop , and extract audio tracks with cd-paranoia . Verify media using dd if=/dev/hdc | md5sum .

Network Utilities (Ethernet & Wi‑Fi)

Display and configure interfaces with ifconfig , bring interfaces up/down with ifup / ifdown , obtain DHCP leases with dhclient , manage routes with route , resolve names with host , nslookup , view interfaces with ip link show , and monitor traffic with netstat or tcpdump .