Master 600 Essential Linux Commands: A Complete Guide for System Administrators

Today we present a comprehensive Linux command summary that includes the most frequently used operations in daily work.

1. Basic Commands

uname -m            # display machine architecture
uname -r            # display kernel version
dmidecode -q        # show hardware components
hdparm -i /dev/hda  # list disk characteristics
hdparm -tT /dev/sda # perform read tests on the disk
arch                # display machine architecture
cat /proc/cpuinfo   # show CPU information
cat /proc/interrupts# show interrupts
cat /proc/meminfo   # check memory usage
cat /proc/swaps     # list active swap devices
cat /proc/version   # display kernel version
cat /proc/net/dev   # show network interfaces and statistics
cat /proc/mounts    # list mounted filesystems
lspci -tv           # list PCI devices
lsusb -tv           # list USB devices
date                # show system date
cal 2007            # display calendar for 2007
clock -w            # write system time to BIOS

2. Shutdown

shutdown -h now            # power off immediately (method 1)
init 0                    # power off (method 2)
telinit 0                 # power off (method 3)
shutdown -h hh:mm         # schedule shutdown
shutdown -c               # cancel scheduled shutdown
shutdown -r now           # reboot immediately
reboot                    # reboot (method 2)
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 personal home directory
cd ~user1                # go to user1's home directory
cd -                     # return to previous directory
pwd                      # show current working directory
ls                       # list files in current directory
ls -F                    # list files with type indicators
ls -l                    # detailed list of files and directories
ls -a                    # show hidden files
ls *[0-9]*               # list files 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 at once
mkdir -p /tmp/dir1/dir2  # create nested directory tree
rm -f file1              # force delete file1
rmdir dir1               # remove empty directory dir1
rm -rf dir1              # recursively delete directory dir1 and its contents
rm -rf dir1 dir2         # delete two directories together
mv dir1 new_dir          # rename or move directory
cp file1 file2           # copy a file
cp dir/* .               # copy all files from dir to current directory
cp -a /tmp/dir1 .        # copy directory preserving attributes
cp -a dir1 dir2          # copy a directory
ln -s file1 lnk1         # create a symbolic link
ln file1 lnk1            # create a hard link
touch -t 0712250000 file1# set file timestamp (YYMMDDhhmm)
file file1               # display MIME type of file
iconv -l                # list known encodings
iconv -f from -t to in > out # 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 files not accessed in last 100 days
find /usr/bin -type f -mtime -10 # find files modified within last 10 days
find / -name \*.rpm -exec chmod 755 "{}" \; # set permissions on .rpm files
find / -xdev -name \*.rpm        # search .rpm files ignoring removable media
locate \*.ps                     # locate .ps files (run updatedb first)
whereis halt                     # locate binary, source, or man page for halt
which halt                       # show full path of executable

5. Mount a Filesystem

mount /dev/hda2 /mnt/hda2               # mount partition hda2
umount /dev/hda2                       # unmount partition hda2
fuser -km /mnt/hda2                    # force unmount when busy
umount -n /mnt/hda2                    # unmount without updating /etc/mtab
mount /dev/fd0 /mnt/floppy              # mount floppy disk
mount /dev/cdrom /mnt/cdrom            # mount CD/DVD
mount /dev/hdc /mnt/cdrecorder          # mount CD‑RW/DVD
mount -o loop file.iso /mnt/cdrom       # mount ISO image
mount -t vfat /dev/hda5 /mnt/hda5       # mount Windows FAT32 filesystem
mount /dev/sda1 /mnt/usbdisk            # mount USB flash 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 human‑readable sizes
ls -lSr | more            # list files sorted by size
du -sh dir1               # estimate disk usage of dir1
du -sk * | sort -rn      # list files/directories by size
rpm -q -a --qf '%10{SIZE}t%{NAME}n' | sort -k1,1n # list installed RPM packages by size
dpkg-query -W -f='${Installed-Size}t${Package}
' | sort -k1,1n # list installed DEB packages by size

7. Users and Groups

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

8. File Permissions (use "+" to set, "-" to remove)

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, rename, or link)
chattr +s file1   # allow safe deletion
chattr +S file1   # force sync after write
chattr +u file1   # allow recovery of a deleted file
lsattr            # list special attributes

9. Special File Attributes (same commands as above)

chattr +a file1
chattr +c file1
chattr +d file1
chattr +i file1
chattr +s file1
chattr +S file1
chattr +u file1
lsattr

10. Archive and Compression

bunzip2 file1.bz2               # decompress .bz2 file
bzip2 file1                     # compress file with bzip2
gunzip file1.gz                 # decompress .gz file
gzip file1                      # compress file with gzip
gzip -9 file1                   # maximum compression
rar a file1.rar test_file       # create .rar archive
rar a file1.rar file1 file2 dir1# add multiple files/dirs to .rar
rar x file1.rar                 # extract .rar archive
unrar x file1.rar               # extract .rar archive
tar -cvf archive.tar file1      # create uncompressed tarball
tar -cvf archive.tar file1 file2 dir1 # create tarball with multiple items
tar -tf archive.tar             # list contents of tarball
tar -xvf archive.tar            # extract tarball
tar -xvf archive.tar -C /tmp    # extract to /tmp
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 # recursively zip multiple items
unzip file1.zip                 # extract zip archive

11. RPM Packages

rpm -ivh package.rpm                # install RPM package
rpm -ivh --nodeps package.rpm       # install ignoring dependencies
rpm -U package.rpm                   # upgrade without changing config files
rpm -F package.rpm                   # update already installed package
rpm -e package_name.rpm              # remove package
rpm -qa                              # list all installed RPMs
rpm -qa | grep httpd                # filter RPMs containing "httpd"
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 package_name --whatrequires   # show packages that depend on this one
rpm -q package_name --whatprovides   # show what this package provides
rpm -q package_name --scripts       # show install/remove scripts
rpm -q package_name --changelog     # show change log
rpm -qf /etc/httpd/conf/httpd.conf  # find which RPM provides a file
rpm -qp package.rpm -l                # list files in an uninstalled RPM
rpm --import /media/cdrom/RPM-GPG-KEY # import GPG key
rpm --checksig package.rpm           # verify package integrity
rpm -V package_name                 # verify package files
rpm -Va                             # verify all installed RPMs (use with care)
rpm -Vp package.rpm                  # verify an uninstalled RPM
rpm2cpio package.rpm | cpio --extract --make-directories *bin* # extract executable from RPM
rpmbuild --rebuild package.src.rpm  # rebuild source RPM

12. YUM Package Manager

yum install package_name            # install package
yum localinstall package.rpm       # install local RPM with dependency resolution
yum update package_name.rpm        # update all installed packages
yum update package_name            # update a specific package
yum remove package_name            # remove a package
yum list                           # list all installed packages
yum search package_name            # search repository for a package
yum clean packages                  # clean downloaded packages
yum clean headers                  # clean header files
yum clean all                      # clean all caches

13. DEB Packages

dpkg -i package.deb                # install or upgrade DEB package
dpkg -r package_name                # remove DEB package
dpkg -l                             # list installed DEB packages
dpkg -l | grep httpd               # filter packages containing "httpd"
dpkg -s package_name                # show package status/info
dpkg -L package_name                # list files provided by package
dpkg --contents package.deb         # list contents of an uninstalled package
dpkg -S /bin/ping                  # find which package provides a file
apt-get install package_name        # install/update DEB package
apt-get update                      # update package index
apt-get upgrade                     # upgrade all installed packages
apt-get remove package_name         # remove DEB package
apt-get check                       # verify package dependencies
apt-get clean                       # clean downloaded package files
apt-cache search searched-package   # search package names

14. View File Contents

cat file1                         # display file from start
tac file1                         # display file from end
more file1                        # paginate long file
less file1                        # paginate with forward/backward navigation
head -2 file1                     # show first two lines
tail -2 file1                     # show last two lines
tail -f /var/log/messages         # follow file growth in real time

15. Text Processing

cat file1 file2 | command > file1_out.txt   # pipe through command (sed, grep, awk, etc.)
grep Aug /var/log/messages                # search for "Aug" in log
grep ^Aug /var/log/messages                # lines starting with "Aug"
grep [0-9] /var/log/messages             # lines containing digits
grep Aug -R /var/log/*                    # recursive search for "Aug"
sed 's/string1/string2/g' example.txt     # replace string1 with string2
sed '/^$/d' example.txt                     # delete empty lines
sed -e '1d' result.txt                     # delete first line
awk 'NR%2==1' example.txt                  # keep odd-numbered lines
paste file1 file2                         # merge files column‑wise
paste -d '+' file1 file2                 # merge with '+' delimiter
sort file1 file2 | uniq                  # unique lines
sort file1 file2 | uniq -u               # lines unique to each file
comm -1 file1 file2                       # show lines only in file2
comm -2 file1 file2                       # show lines only in file1
comm -3 file1 file2                       # show common lines

16. Character Set and File Format Conversion

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 | more                  # list all supported conversions

17. Filesystem Analysis

badblocks -v /dev/hda1               # check for bad blocks
fsck /dev/hda1                       # check/repair ext2/3/4 filesystem
fsck.ext2 /dev/hda1
fsck.ext3 /dev/hda1
fsck.vfat /dev/hda1
fsck.msdos /dev/hda1

18. Initialise a Filesystem

mkfs /dev/hda1                       # create generic filesystem
mke2fs /dev/hda1                     # create ext2 filesystem
mke2fs -j /dev/hda1                  # create ext3 (journaled) filesystem
mkfs -t vfat -F 32 /dev/hda1         # create FAT32 filesystem
fdformat -n /dev/fd0                  # format floppy disk
mkswap /dev/hda3                     # create swap area

19. Swap Filesystem

mkswap /dev/hda3                     # create swap area
swapon /dev/hda3                     # enable swap
swapon /dev/hda2 /dev/hdb3          # enable two swap partitions

20. Backup

dump -0aj -f /tmp/home0.bak /home                # full backup of /home
dump -1aj -f /tmp/home0.bak /home                # interactive backup of /home
restore -if /tmp/home0.bak                      # restore interactive backup
rsync -rogpav --delete /home /tmp                # sync directories
rsync -rogpav -e ssh --delete /home user@host:/tmp # sync over SSH
dd bs=1M if=/dev/hda | gzip | ssh user@host 'dd of=hda.gz' # remote disk backup via SSH
dd if=/dev/sda of=/tmp/file1                     # backup disk to file
tar -Puf backup.tar /home/user                  # incremental backup of /home/user
find /home/user1 -name '*.txt' | xargs cp -av --parents /home/backup/ # copy txt files preserving hierarchy
find /var/log -name '*.log' | tar cv --files-from=- | bzip2 > log.tar.bz2 # archive log files

21. Optical Media

cdrecord -v gracetime=2 dev=/dev/cdrom -eject blank=fast -force # erase rewritable CD
mkisofs /dev/cdrom > cd.iso               # create ISO image from CD
mkisofs -J -R -V "Label CD" -iso-level 4 -o ./cd.iso data_cd # create ISO from directory
cdrecord -v dev=/dev/cdrom cd.iso        # burn ISO to CD
gzip -dc cd_iso.gz | cdrecord dev=/dev/cdrom # burn compressed ISO
mount -o loop cd.iso /mnt/iso           # mount ISO image
cd-paranoia -B                           # extract audio tracks to WAV
dd if=/dev/hdc | md5sum                  # compute MD5 of CD device

22. Network (Ethernet and Wi‑Fi)

ifconfig eth0                         # show Ethernet config
ifup eth0                            # enable interface
ifdown eth0                          # disable interface
ifconfig eth0 192.168.1.1 netmask 255.255.255.0 # set static IP
ifconfig eth0 promisc                # enable promiscuous mode
dhclient eth0                        # obtain IP via DHCP
route -n                             # show routing table
route add -net 0/0 gw IP_Gateway     # set default gateway
route add -net 192.168.0.0 netmask 255.255.0.0 gw 192.168.1.1 # static route
echo 1 > /proc/sys/net/ipv4/ip_forward # enable IP forwarding
hostname                             # show hostname
host www.example.com                 # DNS lookup
nslookup www.example.com            # DNS lookup (alternative)
ip link show                         # list network interfaces
mii-tool eth0                        # show link status
ethtool eth0                         # show interface statistics
netstat -tup                         # list active connections with PID
netstat -tupl                        # list listening services with PID
tcpdump tcp port 80                  # capture HTTP traffic
iwlist scan                          # scan Wi‑Fi networks
iwconfig eth1                        # show wireless interface config
whois www.example.com                # query WHOIS database

23. List Directory Contents

ls -a                               # show all files including hidden
ls -l                               # detailed list
ls -R                               # recursive listing
ls -ld                              # list directory info
pwd                                 # show current directory

24. View File Type

file filename                        # display file type

25. Copy Files and Directories

cp -r source_dir target_dir          # recursively copy directory
cp -a source_dir target_dir          # copy preserving attributes

26. Common System Commands

date                                 # view or set system date/time
cal                                  # display calendar
uptime                               # show system uptime

27. VIM

VIM is a powerful command‑line text editor. Use vim filename to open a file, :q to quit, and :w to save. It supports three modes: command, insert, and ex.

28. RPM Package Management Commands

rpm -ivh package.rpm                # install package
rpm -e package_name                 # remove package (keeps modified config files)
rpm -Uvh package.rpm                # upgrade package
rpm -Fvh package.rpm                # update package if newer version exists
rpm -q package_name                 # query installed package
rpm -ql package_name                # list files provided by package

29. Final Note

Errors may exist due to my limited knowledge; I welcome corrections. Thank you all, and see you again!