600 Essential Linux Commands Every Sysadmin Should Know

1. Basic Commands

uname -m            # display processor architecture
uname -r            # display kernel version
arch                # display processor architecture
cat /proc/cpuinfo   # show CPU info
cat /proc/interrupts
cat /proc/meminfo   # check memory usage
cat /proc/swaps     # show swap usage
cat /proc/version   # show kernel version
cat /proc/net/dev   # show network interfaces and statistics
cat /proc/mounts    # show mounted filesystems
lspci -tv           # list PCI devices
lsusb -tv           # list USB devices
date                # show system date
cal 2007            # display calendar for 2007
date 041217002007.00 # set date and time (MMDDhhmmYYYY.ss)
clock -w            # write system time to BIOS

2. Shutdown and Reboot

shutdown -h now    # power off immediately
init 0              # power off (alternative)
telinit 0           # power off (alternative)
shutdown -h HH:MM   # schedule shutdown at specific time
shutdown -c         # cancel scheduled shutdown
shutdown -r now    # reboot immediately
reboot              # reboot (alternative)
logout              # log out

3. Files and Directories

cd /home            # change to /home directory
cd ..               # go up one level
cd ../..            # go up two levels
cd                  # go to home directory
cd ~user1           # go to user1's home directory
cd -                # return to previous directory
pwd                 # show current working directory
ls                  # list files
ls -F               # list files with type indicators
ls -l               # detailed list
ls -a               # show hidden files
ls *[0-9]*          # list files/directories containing numbers
tree                # display directory tree (method 1)
lstree              # display directory tree (method 2)
mkdir dir1          # create directory dir1
mkdir dir1 dir2     # create two directories
mkdir -p /tmp/dir1/dir2   # create nested directories
rm -f file1         # force delete file1
rmdir dir1          # remove empty directory dir1
rm -rf dir1         # remove directory and its contents recursively
mv dir1 new_dir     # rename or move directory
cp file1 file2      # copy file
cp dir/* .          # copy all files from dir to current directory
cp -a /tmp/dir1 .   # copy directory preserving attributes
ln -s file1 lnk1    # create symbolic link
ln file1 lnk1       # create hard link
touch -t 0712250000 file1   # set file timestamp (YYMMDDhhmm)
file file1          # display MIME type of file
iconv -l            # list known encodings
iconv -f fromEncoding -t toEncoding inputFile > outputFile   # convert file encoding
find . -maxdepth 1 -name *.jpg -print -exec convert "{}" -resize 80x60 "thumbs/{}" \;   # batch resize images

4. File Search

find / -name file1               # search from root for file1
find / -user user1               # search files owned by user1
find /home/user1 -name *.bin    # search for .bin files in /home/user1
find /usr/bin -type f -atime +100   # find executables not accessed in 100 days
find /usr/bin -type f -mtime -10    # find files modified in last 10 days
find / -name *.rpm -exec chmod 755 '{}' \;   # set permissions on .rpm files
find / -xdev -name *.rpm        # search .rpm files ignoring removable devices
locate *.ps                     # locate .ps files (requires updatedb)
whereis halt                    # locate binary, source, and man page for halt
which halt                      # show full path of executable

5. Mounting Filesystems

mount /dev/hda2 /mnt/hda2                # mount partition hda2
umount /dev/hda2                         # unmount partition
fuser -km /mnt/hda2                      # force unmount if busy
umount -n /mnt/hda2                      # unmount without updating /etc/mtab
mount /dev/fd0 /mnt/floppy               # mount floppy
mount /dev/cdrom /mnt/cdrom             # mount CD/DVD
mount /dev/hdc /mnt/cdrecorder           # mount CD-RW/DVD-RW
mount -o loop file.iso /mnt/cdrom         # mount ISO image
mount -t vfat /dev/hda5 /mnt/hda5        # mount FAT32 filesystem
mount /dev/sda1 /mnt/usbdisk             # mount USB drive
mount -t smbfs -o username=user,password=pass //WinClient/share /mnt/share   # mount Windows share

6. Disk Space

df -h                     # show mounted partitions with sizes
ls -lSr | more           # list files sorted by size
du -sh dir1               # estimate disk usage of dir1
du -sk * | sort -rn      # list directories/files by size
rpm -q -a --qf '%10{SIZE}t%{NAME}
' | sort -k1,1n   # list installed RPM packages by size (RPM/Fedora)
dpkg-query -W -f='${Installed-Size;10}t${Package}
' | sort -k1,1n   # list installed DEB packages by size (Debian/Ubuntu)

7. Users and Groups

groupadd group_name      # create new group
groupdel group_name      # delete group
groupmod -n new_group_name old_group_name   # rename group
useradd -c "Name Surname" -g admin -d /home/user1 -s /bin/bash user1   # create user in admin group
useradd user1           # create new user
userdel -r user1         # delete user and home directory
usermod -c "User FTP" -g system -d /ftp/user1 -s /sbin/nologin user1   # modify user attributes
passwd                  # change password (root only for other users)
passwd user1             # change password for user1
chage -E 2005-12-31 user1   # set password expiration date
pwck                     # verify /etc/passwd format
grpck                    # verify /etc/group format
newgrp group_name        # switch to new group for file creation

8. File Permissions

ls -lh                   # list with human‑readable permissions
chmod ugo+rwx directory1 # give read/write/execute to user, group, others
chmod go-rwx directory1 # remove permissions from group and others
chown user1 file1        # change file owner
chown -R user1 directory1   # change owner recursively
chgrp group1 file1       # change group ownership
chown user1:group1 file1 # change both owner and group
find / -perm -u+s       # list files with SUID bit set
chmod u+s /bin/file1    # set SUID on binary
chmod u-s /bin/file1    # remove SUID
chmod g+s /home/public  # set SGID on directory
chmod g-s /home/public  # remove SGID
chmod o+t /home/public  # set sticky bit
chmod o-t /home/public  # remove sticky bit
chmod +x file           # add execute permission
chmod -x file           # remove execute permission

9. Special File Attributes

chattr +a file1   # allow only append writes
chattr +c file1   # enable automatic compression
chattr +d file1   # exclude from dump backups
chattr +i file1   # make immutable (cannot delete/modify)
chattr +s file1   # secure deletion
chattr +S file1   # sync writes immediately
chattr +u file1   # allow undeletion
lsattr            # list file attributes

10. Archiving and Compression

bunzip2 file1.bz2          # decompress bzip2 file
bzip2 file1                # compress file with bzip2
gunzip file1.gz            # decompress gzip file
gzip file1                 # compress file with gzip
gzip -9 file1              # maximum compression
rar a file1.rar test_file  # create RAR archive
rar x file1.rar            # extract RAR archive
unrar x file1.rar          # extract RAR archive
tar -cvf archive.tar file1                 # create uncompressed tarball
tar -tf archive.tar        # list contents of tarball
tar -xvf archive.tar       # extract tarball
tar -cvfj archive.tar.bz2 dir1   # create bzip2‑compressed tarball
tar -xvfj archive.tar.bz2          # extract bzip2 tarball
tar -cvfz archive.tar.gz dir1       # create gzip‑compressed tarball
tar -xvfz archive.tar.gz            # extract gzip tarball
zip file1.zip file1                # create zip archive
zip -r file1.zip file1 file2 dir1  # zip multiple files/directories
unzip file1.zip                    # extract zip archive

11. RPM Package Management

rpm -ivh package.rpm                # install RPM package
rpm -ivh --nodeps package.rpm       # install ignoring dependencies
rpm -U package.rpm                  # upgrade package without changing config files
rpm -F package.rpm                  # upgrade already‑installed package
rpm -e package_name.rpm             # erase package
rpm -qa                             # list all installed RPMs
rpm -qa | grep httpd               # filter installed packages
rpm -qi package_name               # query detailed info
rpm -ql package_name               # list files provided by package
rpm -qc package_name               # list config files of package
rpm -q --whatrequires package_name # show packages that depend on this one
rpm -V package_name                # verify package files
rpm --import /path/to/RPM-GPG-KEY # import GPG key
rpm --checksig package.rpm         # verify package signature

12. YUM Package Manager

yum install package_name            # install package
yum localinstall package.rpm        # install local RPM with dependency resolution
yum update package_name            # update package
yum remove package_name             # remove package
yum list                            # list all packages
yum search package_name             # search repository
yum clean packages                  # clean package cache
yum clean all                      # clean all caches

13. DEB Package Management

dpkg -i package.deb                 # install or upgrade DEB package
dpkg -r package_name                # remove package
dpkg -l                             # list installed DEB packages
dpkg -s package_name                # show status of package
dpkg -L package_name                 # list files installed by package
apt-get install package_name        # install package via APT
apt-get update                      # update package index
apt-get upgrade                     # upgrade all upgradable packages
apt-get remove package_name         # remove package
apt-cache search keyword            # search package names

14. Viewing File Contents

cat file1                         # display file
tac file1                         # display file in reverse order
more file1                        # paginate long file
less file1                        # paginate with backward navigation
head -2 file1                     # show first two lines
tail -2 file1                     # show last two lines
tail -f /var/log/messages         # follow appended output

15. Text Processing

grep pattern file                 # search for pattern in file
sed 's/old/new/g' file           # replace text
awk '{print $1}' file            # field extraction
tr '[:lower:]' '[:upper:]' < file # translate case
sort file                         # sort lines
uniq file                         # filter duplicate lines
comm file1 file2                 # compare two files

16. Character Set Conversion and File Format

dos2unix filedos.txt fileunix.txt   # convert DOS to UNIX line endings
unix2dos fileunix.txt filedos.txt   # convert UNIX to DOS line endings
recode ..HTML < page.txt > page.html   # convert text to HTML
recode -l                         # list supported conversions

17. Filesystem Analysis

badblocks -v /dev/hda1            # check for bad blocks
fsck /dev/hda1                    # check/repair filesystem
fsck.ext2 /dev/hda1               # check/repair ext2 filesystem
fsck.ext3 /dev/hda1               # check/repair ext3 filesystem
fsck.vfat /dev/hda1               # check/repair FAT filesystem

18. Initializing a Filesystem

mkfs /dev/hda1                    # create generic filesystem
mke2fs /dev/hda1                 # create ext2 filesystem
mke2fs -j /dev/hda1              # create ext3 (with journaling)
mkfs -t vfat /dev/hda1           # create FAT32 filesystem
fdformat -n /dev/fd0             # format floppy
mkswap /dev/hda3                  # create swap area

19. Swap Filesystem

mkswap /dev/hda3                 # create swap partition
swapon /dev/hda3                 # enable swap
swapon /dev/hda2 /dev/hdb3       # enable multiple swap partitions

20. Backup

dump -0aj -f /tmp/home0.bak /home   # full backup of /home
dump -1aj -f /tmp/home0.bak /home   # incremental backup of /home
restore -if /tmp/home0.bak           # restore incremental backup
rsync -rogpav --delete /home /tmp    # sync directories
rsync -az -e ssh --delete ip:/home /local   # remote sync with compression
dd if=/dev/sda of=/tmp/file1        # copy raw disk to file
tar -Puf backup.tar /home/user      # interactive backup with tar
(cd /tmp/local && tar c .) | ssh user@host 'cd /home/share && tar x -p'   # copy directory over SSH

21. CD/DVD Operations

cdrecord -v gracetime=2 dev=/dev/cdrom -eject blank=fast -force   # erase rewritable CD
mkisofs /dev/cdrom > cd.iso                                 # create ISO image
mkisofs -J -R -V "Label CD" -o ./cd.iso data_cd            # create ISO with Joliet and Rock Ridge
cdrecord -v dev=/dev/cdrom cd.iso                         # burn ISO to CD
mount -o loop cd.iso /mnt/iso                               # mount ISO image

22. Networking (Ethernet and Wi‑Fi)

ifconfig eth0                     # show Ethernet config
ifup eth0                         # bring interface up
ifdown eth0                       # bring interface down
ifconfig eth0 192.168.1.1 netmask 255.255.255.0   # set static IP
dhclient eth0                     # obtain IP via DHCP
route -n                         # show routing table
route add -net 0/0 gw IP_Gateway  # set default gateway
hostname                         # show hostname
host www.example.com              # DNS lookup
nslookup www.example.com           # DNS lookup (alternative)
netstat -tup                     # list active connections with PIDs
tcpdump tcp port 80               # capture HTTP traffic
iwlist scan                      # scan Wi‑Fi networks
iwconfig eth1                     # show wireless interface config

23. Listing Directory Contents

ls -a            # all files including hidden
ls -l            # detailed list
ls -R            # recursive list
ls -ld           # list directory itself
pwd              # print working directory

24. Determining File Type

file filename    # display file type

25. Copying Files and Directories

cp source dest                 # copy file or directory
cp -r src_dir dest_dir        # recursive copy of directory tree

26. Common System Commands

date                         # view or set system date/time
hwclock                      # view hardware clock (requires root)
cal                          # display calendar
uptime                       # show system uptime
echo "text" >> file          # append text to file
cat file                     # display file content
cat file1 file2 > combined    # concatenate files
head -n 10 file              # first 10 lines
tail -n 10 file              # last 10 lines
tail -f file                 # follow file growth
more file                    # paginate forward only
less file                    # paginate with backward navigation
ls -al | less               # long list with paging
dmesg                        # kernel ring buffer messages
df -h                        # disk space usage
du -sh dir                   # summarize disk usage of directory
free -h                      # memory usage

27. VIM Editor

vim file                     # open file in VIM
:i                           # insert mode before cursor
:o                           # insert mode on new line below
:dd                          # delete current line
:yy                          # yank (copy) current line
:n+yy                        # yank n lines
:p                           # paste after cursor
:u                           # undo last change
:r                           # replace character under cursor
:/pattern                    # search for pattern
:!command                    # execute external command
:qa                          # quit all windows
: wq                         # write and quit
:set number                  # show line numbers

28. RPM Package Management Commands

rpm -ivh package.rpm          # install package (show progress)
rpm -e package_name           # erase package (keeps modified config files)
rpm -Uvh package.rpm          # upgrade package (replace older version)
rpm -Fvh package.rpm          # update package (only if newer)
rpm -q package_name           # query installed package
rpm -ql package_name          # list files provided by package
rpm -qi package_name          # detailed info about package

29. Software Package Management (RPM)

rpm –ivh wu-ftpd-2.6.2-8.i386.rpm   # install example package
rpm –e wu-ftpd                     # erase example package
rpm –Uvh wu-ftpd-2.6.2-8.i386.rpm   # upgrade example package
rpm –Fvh wu-ftpd-2.6.2-8.i386.rpm   # update example package if newer
rpm –q wu-ftpd                     # query package info
rpm –ql xv                         # list files of package xv