Linux Command — System Information
Command Code Comment Description
arch Displays the processor architecture of the machine (1)
uname -m Displays the processor architecture of the machine (2)
uname -r Display the version of the kernel currently in use
dmidecode -q Display hardware system components - (SMBIOS / DMI)
hdparm -i /dev/hda List the architectural characteristics of a disk
hdparm -tT /dev/sda Perform a test read operation on the disk
cat /proc/cpuinfo Display CPU information
cat /proc/interrupts Display interrupts
cat /proc/meminfo Check memory usage
cat /proc/swaps Display which swaps are being used
cat /proc/version Display the version of the kernel
cat /proc/net/dev Display network adapters and statistics
cat /proc/mounts Display loaded file systems
lspci -tv List PCI devices
lsusb -tv Display USB devices
date Display system date
cal 2007 Display the calendar for the year 2007
date 041217002007.00 Set the date and time - month day hour minute year.second
clock -w Save the time change to BIOS
Linux Commands — System Shutdown (Shutdown, Restart, and Logout)
Command Code Comment Description
shutdown -h now Shutdown the system
init Shutdown the system
telinit Shutdown the system
shutdown -h hours:minutes & Shutdown the system at a scheduled time
shutdown -c Cancel the scheduled system shutdown
shutdown -r now Restart
reboot Restart
logout Logout
Linux Commands — Files and Directories
Command Code Comment Description
cd /home Enter the '/home' directory'
cd .. Return to the parent directory
cd ../.. Return to the directory two levels up
cd Enter the user's home directory
cd ~user1 Enter the user's home directory
cd - Return to the last directory you were in
pwd Print the working directory
ls List the contents of a directory
ls -F List the contents of a directory
ls -l Display detailed information about files and directories
ls -a List all files, including hidden ones
ls *[-9]* List files and directories that contain numbers in their names
tree Display the directory tree starting from the root directory
lstree Display the directory tree starting from the root directory
mkdir dir1 Create a directory named 'dir1'
mkdir dir1 dir2 Create two directories at the same time
mkdir -p /tmp/dir1/dir2 Create a directory tree
rm -f file1 Remove a file named 'file1'
rmdir dir1 Remove a directory named 'dir1'
rm -rf dir1 Remove a directory named 'dir1' and its contents
rm -rf dir1 dir2 Remove two directories and their contents at the same time
mv dir1 new_dir Rename/move a directory
cp file1 file2 Copy a file
cp dir/* . Copy all files from a directory to the current working directory
cp -a /tmp/dir1 . Copy a directory to the current working directory
cp -a dir1 dir2 Copy a directory
ln -s file1 lnk1 Create a symbolic link pointing to a file or directory
ln file1 lnk1 Create a hard link pointing to a file or directory
touch -t 712250000 file1 Change the timestamp of a file or directory - (YYMMDDhhmm)
iconv -l List known encodings
iconv -f fromEncoding -t toEncoding inputFile > outputFile Change the encoding of characters
find . -maxdepth 1 -name *.jpg -print -exec convert Batch resize files in the current directory and send them to the thumbnail directory (requires ImageMagick conversion)
Linux Commands — File Search
Command Code Explanation
find / -name file1 Search for files and directories starting from the root file system '/'
find / -user user1 Search for files and directories owned by user 'user1'
find /home/user1 -name \*.bin Search for files ending with '.bin' in the directory '/home/user1'
find /usr/bin -type f -atime +100 Search for executable files that have not been used in the past 100 days
find /usr/bin -type f -mtime -10 Search for files that have been created or modified within the last 10 days
find / -name \*.rpm -exec chmod 755 '{}' \; Search for files ending with '.rpm' and set their permissions
find / -xdev -name \*.rpm Search for files ending with '.rpm', ignoring removable devices such as optical drives and flash drives
locate \*.ps Find files ending with '.ps' - run the 'updatedb' command first
whereis halt Display the location of a binary, source code, or man page
which halt Display the full path of a binary or executable file
Linux Commands — Mount a File System
Command Code Explanation
mount /dev/hda2 /mnt/hda2 Mount a disk called hda2 - Ensure the directory '/mnt/hda2' exists
umount /dev/hda2 Unmount a disk called hda2 - Exit from the mount point '/mnt/hda2' first
fuser -km /mnt/hda2 Force unmount when the device is busy
umount -n /mnt/hda2 Perform the unmount operation without writing to the /etc/mtab file - Very useful when the file is read-only or when the disk is full
mount /dev/fd /mnt/floppy Mount a floppy disk
mount /dev/cdrom /mnt/cdrom Mount a CD-ROM or DVD-ROM
mount /dev/hdc /mnt/cdrecorder Mount a CD-RW or DVD-ROM
mount /dev/hdb /mnt/cdrecorder Mount a CD-RW or DVD-ROM
mount -o loop file.iso /mnt/cdrom Mount a file or ISO image file
mount -t vfat /dev/hda5 /mnt/hda5 Mount a Windows FAT32 file system
mount /dev/sda1 /mnt/usbdisk Mount a USB flash drive or flash memory device
mount -t smbfs -o username=user,password=pass //WinClient/share /mnt/share Mount a Windows network share
Linux Commands — Disk Space
Command Code Comment Description
df -h Display the list of mounted partitions
ls -lSr |more Arrange files and directories by size
du -sh dir1 Estimate the disk space used by the directory 'dir1'
du -sk * | sort -rn Display the size of files and directories in order of capacity
rpm -q -a --qf '%10{SIZE}t%{NAME}n' | sort -k1,1n Display the space used by installed rpm packages in order of size (Fedora, Red Hat-like systems)
dpkg-query -W -f='${Installed-Size;10}t${Package}n' | sort -k1,1n Display the space used by installed deb packages in order of size (Ubuntu, Debian-like systems)
Linux Commands — Users and Groups
Command Code Comment Description
groupadd group_name Create a new group
groupdel group_name Delete a group
groupmod -n new_group_name old_group_name Rename a group
useradd -c "Name Surname" -g admin -d /home/user1 -s /bin/bash user1 Create a user belonging to the "admin" group
useradd user1 Create a new user
userdel -r user1 Delete a user ('-r' to exclude the home directory)
usermod -c "User FTP" -g system -d /ftp/user1 -s /bin/nologin user1 Modify user attributes
passwd Modify password
passwd user1 Modify a user's password (only allowed for root to execute)
chage -E 202-12-31 user1 Set the expiration date for a user's password
pwck Check the '/etc/passwd' file format and syntax correction, as well as existing users
grpck Check the '/etc/passwd' file format and syntax correction, as well as existing groups
newgrp group_name Log in to a new group to change the default group of newly created files
Linux Commands — File Permissions - Use "+" to set permissions, use "-" to cancel
Command Code Comment Explanation
ls -lh Display permissions
ls /tmp | pr -T5 -W$COLUMNS Divide the terminal into 5 columns for display
chmod ugo+rwx directory1 Set read (r), write (w), and execute (x) permissions for everyone (u), group (g), and others (o) on a directory
chmod go-rwx directory1 Remove read, write, and execute permissions for the group (g) and others (o) on a directory
chown user1 file1 Change the ownership of a file
chown -R user1 directory1 Change the ownership of a directory and all files within it
chgrp group1 file1 Change the group of a file
chown user1:group1 file1 Change the owner and group of a file
find / -perm -u+s List all files in the system that use SUID control
chmod u+s /bin/file1 Set the SUID bit for a binary file - the user running the file is given the same permissions as the owner
chmod u-s /bin/file1 Disable the SUID bit for a binary file
chmod g+s /home/public Set the SGID bit for a directory - similar to SUID, but for directories
chmod g-s /home/public Disable the SGID bit for a directory
chmod o+t /home/public Set the STIKY bit for a file - only the legitimate owner can delete the file
chmod o-t /home/public Disable the STIKY bit for a directory
Linux Commands — Special File Attributes - Use "+" to set permissions, use "-" to cancel
Command Code Comment Explanation
chattr +a file1 Only allow appending to the file
chattr +c file1 Allow the file to be automatically compressed/decompressed by the kernel
chattr +d file1 During file system backup, the dump utility will ignore this file
chattr +i file1 Set the file to be immutable, cannot be deleted, modified, renamed, or linked
chattr +s file1 Allow a file to be safely deleted
chattr +S file1 Once an application writes to this file, make the system immediately write the modified results to the disk
chattr +u file1 If the file is deleted, the system will allow you to recover the deleted file later
lsattr Display special attributes
Linux Command — File Packing and Compression
Command Code Comments
bunzip2 file1.bz2 Unzip a file called 'file1.bz2'
bzip2 file1 Compresses a file called 'file1'
gunzip file1.gz Unzip a file called 'file1.gz'
gzip file1 Compresses a file called 'file1'
gzip -9 file1 Maximum compression
rar a file1.rar test_file Create a package called 'file1.rar'
rar a file1.rar file1 file2 dir1 Compresses 'file1', 'file2', and the directory 'dir1' at the same time
rar x file1.rar Unzip rar package
unrar x file1.rar Unzip rar package
tar -cvf archive.tar file1 Create an uncompressed tarball
tar -cvf archive.tar file1 file2 dir1 Create an archive file containing 'file1', 'file2', and 'dir1'
tar -tf archive.tar Display the contents of a package
tar -xvf archive.tar Release a package
tar -xvf archive.tar -C /tmp Release the compressed package to the /tmp directory
tar -cvfj archive.tar.bz2 dir1 Create a bzip2 compressed package
tar -jxvf archive.tar.bz2 Unzip a bzip2 compressed package
tar -cvfz archive.tar.gz dir1 Create a gzip compressed package
tar -zxvf archive.tar.gz Unzip a gzip compressed package
zip file1.zip file1 Create a zip compressed package
zip -r file1.zip file1 file2 dir1 Compresses several files and directories into a zip compressed package at the same time
unzip file1.zip Unzip a zip compressed package
Linux Commands — RPM Package - (Fedora, Redhat and similar systems)
Command Code Comment Description
rpm -ivh package.rpm Install an RPM package
rpm -ivh --nodeeps package.rpm Install an RPM package ignoring dependency warnings
rpm -U package.rpm Update an RPM package without altering its configuration files
rpm -F package.rpm Update a specifically installed RPM package
rpm -e package_name.rpm Remove an RPM package
rpm -qa Display all installed RPM packages in the system
rpm -qa | grep httpd Display all RPM packages with "httpd" in their names
rpm -qi package_name Obtain special information about an installed package
rpm -qg "System Environment/Daemons" Display the RPM package of a component
rpm -ql package_name Display the list of files provided by an installed RPM package
rpm -qc package_name Display the list of configuration files provided by an installed RPM package
rpm -q package_name --whatrequires Display the list of packages that have a dependency on an RPM package
rpm -q package_name --whatprovides Display the disk space occupied by an RPM package
rpm -q package_name --scripts Display the scripts executed during installation/deletion
rpm -q package_name --changelog Display the modification history of an RPM package
rpm -qf /etc/httpd/conf/httpd.conf Identify which RPM package provides the given file
rpm -qp package.rpm -l Display the list of files provided by an uninstalled RPM package
rpm --import /media/cdrom/RPM-GPG-KEY Import a public key digital certificate
rpm --checksig package.rpm Confirm the integrity of an RPM package
rpm -qa gpg-pubkey Confirm the integrity of all installed RPM packages
rpm -V package_name Check file size, permissions, type, owner, group, MD5 checksum, and last modification time
rpm -Va Check all installed RPM packages in the system - use with caution
rpm -Vp package.rpm Verify that an RPM package is not yet installed
rpm2cpio package.rpm | cpio --extract --make-directories *bin* Execute executable files from an RPM package
rpm -ivh /usr/src/redhat/RPMS/`arch`/package.rpm Install a built package from an RPM source
rpmbuild --rebuild package_name.src.rpm Build an RPM package from RPM source
Linux Commands — YUM Package Manager - (Fedora, RedHat, CentOS, etc.)
Command Code Comment Description
yum install package_name Install a package using yum, resolving dependencies automatically
yum update Update all installed packages to their latest versions
yum update package_name Update a specific package to its latest version
yum remove package_name Remove a package and its dependencies that were installed with it
yum list available List all available packages from repositories
yum search keyword Search for packages by keyword
yum info package_name Display detailed information about a package
yum clean all Clean up cache and metadata to free disk space
yum groupinstall group_name Install a package group
yum groupremove group_name Remove a package group
yum check-update Check for available updates without applying them
Linux Command — YUM Package Upgrader - (Fedora, RedHat and similar systems)
Command Code Comment Description
yum install package_name Download and install an rpm package
yum localinstall package_name.rpm Install an rpm package, using your own software repository to resolve all dependencies
yum update package_name.rpm Update all installed rpm packages in the current system
yum update package_name Update an rpm package
yum remove package_name Delete an rpm package
yum list List all packages currently installed in the system
yum search package_name Search for a software package in the rpm repository
yum clean packages Clean the rpm cache and delete downloaded packages
yum clean headers Delete all header files
yum clean all Delete all cached packages and header files
Linux Command — DEB Package (Debian, Ubuntu and similar systems)
Command Code Comment Explanation
dpkg -i package.deb Install/Update a deb package
dpkg -r package_name Remove a deb package from the system
dpkg -l Display all deb packages that have been installed in the system
dpkg -l | grep httpd Display all deb packages that contain the word "httpd"
dpkg -s package_name Get information about a specific package that has been installed in the system
dpkg -L package_name Display the list of files provided by an installed deb package in the system
dpkg --contents package.deb Display the list of files provided by an uninstalled package
dpkg -S /bin/ping Confirm which deb package provides the given file
Linux Command — APT Software Tool (Debian, Ubuntu and similar systems)
Command Code Comment Explanation
apt-get install package_name Install/Update a deb package
apt-cdrom install package_name Install/Update a deb package from a CD-ROM
apt-get update Upgrade the software packages in the list
apt-get upgrade Upgrade all installed software
apt-get remove package_name Remove a deb package from the system
apt-get check Confirm that the dependency software repository is correct
apt-get clean Clean the cache from downloaded software packages
apt-cache search searched-package Return the names of software packages that contain the search string
Linux Command — View File Contents
Command Code Comment Explanation
cat file1 View the contents of the file from the first byte in the forward direction
tac file1 View the contents of a file in reverse from the last line
more file1 View the contents of a long file
less file1 Similar to the 'more' command, but it allows reverse operations in the file like forward operations
head -2 file1 View the first two lines of a file
tail -2 file1 View the last two lines of a file
tail -f /var/log/messages Real-time view of the content being added to a file
Linux Commands — Text Processing
Command Code Comment Explanation
cat file1 | command( sed, grep, awk, grep, etc...) > result.txt Merge the detailed explanation text of a file and write the summary into a new file
cat file1 | command( sed, grep, awk, grep, etc...) >> result.txt Merge the detailed explanation text of a file and write the summary into an existing file
grep Aug /var/log/messages Search for the keyword "Aug" in the file '/var/log/messages'
grep ^Aug /var/log/messages Find words starting with "Aug" in the file '/var/log/messages'
grep [-9] /var/log/messages Select all lines in the '/var/log/messages' file that contain numbers
grep Aug -R /var/log/* Search for the string "Aug" in the directory '/var/log' and subsequent directories
sed 's/stringa1/stringa2/g' example.txt Replace "string1" with "string2" in the example.txt file
sed '/^$/d' example.txt Delete all blank lines from the example.txt file
sed '/ *#/d; /^$/d' example.txt From example.txt Delete all comments and blank lines in the file
echo 'esempio' | tr '[:lower:]' '[:upper:]' Merge the content of the upper and lower cells
sed -e '1d' result.txt Exclude the first line from the file example.txt
sed -n '/stringa1/p' View lines that only contain the word "string1"
sed -e 's/ *$//' example.txt Delete the blank characters at the end of each line
sed -e 's/stringa1//g' example.txt Delete only the word "string1" from the document and keep the rest
sed -n '1,5p;5q' example.txt View content from the first line to the 5th line
sed -n '5p;5q' example.txt View the 5th line
sed -e 's/00*//g' example.txt Replace multiple zeros with a single zero
cat -n file1 Mark the line numbers of the file
cat example.txt | awk 'NR%2==1' Delete all even lines in the example.txt file
echo a b c | awk '{print $1}' View the first column of a line
echo a b c | awk '{print $1,$3}' View the first and third columns of a line
paste file1 file2 Merge the contents of two files or two columns
paste -d '+' file1 file2 Merge the contents of two files or two columns, separated by "+"
sort file1 file2 Sort the contents of two files
sort file1 file2 | uniq Extract the union of two files (duplicate lines are kept only once)
sort file1 file2 | uniq -u Delete the intersection, leave the other lines
sort file1 file2 | uniq -d Extract the intersection of two files (only keep the files that exist in both files)
comm -1 file1 file2 Compare the contents of two files and delete the contents contained in 'file1' only
comm -2 file1 file2 Compare the contents of two files and delete the contents contained in 'file2' only
comm -3 file1 file2 Compare the contents of two files and delete the common parts of both files
Linux Commands — Character Setting and File Format Conversion
Command Code Comment Description
dos2unix filedos.txt fileunix.txt Convert the format of a text file from MSDOS to UNIX
unix2dos fileunix.txt filedos.txt Convert the format of a text file from UNIX to MSDOS
recode ..HTML < page.txt > page.html Convert a text file to HTML
recode -l | more Display all allowed conversion formats
Linux Commands — File System Analysis
Command Code Comment Description
badblocks -v /dev/hda1 Check for bad blocks on the hda1 disk
fsck /dev/hda1 Repair/Check the integrity of the Linux file system on the hda1 disk
fsck.ext2 /dev/hda1 Repair/Check the integrity of the ext2 file system on the hda1 disk
e2fsck /dev/hda1 Repair/Check the integrity of the ext2 file system on the hda1 disk
e2fsck -j /dev/hda1 Repair/Check the integrity of the ext3 file system on the hda1 disk
fsck.ext3 /dev/hda1 Repair/Check the integrity of the ext3 file system on the hda1 disk
fsck.vfat /dev/hda1 Restore the MBR content from the backup that has been saved to a floppy disk
Linux Command — CD-ROM
Command Code Comment Description
cdrecord -v gracetime=2 dev=/dev/cdrom -eject blank=fast -force Erase the content of a rewritable CD
mkisofs /dev/cdrom > cd.iso Create an ISO image file of a CD on the disk
mkisofs /dev/cdrom | gzip > cd_iso.gz Create a compressed ISO image file of a CD on the disk
mkisofs -J -allow-leading-dots -R -V "Label CD" -iso-level 4 -o ./cd.iso data_cd Create an ISO image file of a directory
cdrecord -v dev=/dev/cdrom cd.iso Burn an ISO image file
gzip -dc cd_iso.gz | cdrecord dev=/dev/cdrom - Burn a compressed ISO image file
mount -o loop cd.iso /mnt/iso Mount an ISO image file
cd-paranoia -B Transfer audio tracks from a CD to wav files
cd-paranoia -- "-3" Transfer audio tracks from a CD to wav files (parameter -3)
cdrecord --scanbus Scan the bus to identify SCSI channels
dd if=/dev/hdc | md5sum Check the md5sum code of a device, such as a CD
Linux Command — Network - (Ethernet and WIFI Wireless)
Command Code Comment Description
dhclient eth Enable the 'eth' network device in DHCP mode
ethtool eth Display traffic statistics of the network card 'eth'
host www.example.com Find the hostname to resolve the name and IP address and mirror
hostname Display the hostname
ifconfig eth Display the configuration of an Ethernet card
ifconfig eth 192.168.1.1 netmask 255.255.255. Control the IP address
ifconfig eth promisc Set 'eth' to promiscuous mode to sniff packets (sniffing)
ifdown eth Disable a 'eth' network device
ifup eth Enable a 'eth' network device
ip link show Display the connection status of all network devices
iwconfig eth1 Display the configuration of a wireless network card
iwlist scan Display wireless networks
mii-tool eth Display the connection status of 'eth'
netstat -tup Display all enabled network connections and their PID
netstat -tup1 Display all listening network services and their PIDs
netstat -rn Display routing table, similar to the "route -n" command
nslookup www.example.com Resolve hostnames to map names to IP addresses and mirrors
route -n Display routing table
route add -net 0/0 gw IP_Gateway Control the default gateway
route add -net 192.168.0.0 netmask 255.255.0.0 gw 192.168.1.1 Control static routing to the network '192.168.0.0/16'
route del 0/0 gw IP_gateway Delete static route
echo "1"> /proc/sys/net/ipv4/ip_forward Enable IP forwarding
tcpdump tcp port 80 Display all HTTP loopbacks
whois www.example.com Lookup in the Whois database
Linux Commands — Microsoft Windows Networking
Command Code Comment Description
mount -t smbfs -o username=user,password=pass //WinClient/share/mnt/share Mount a Windows network share
nbtscan ip addr NetBIOS name resolution
nmblookup -A ip addr NetBIOS name resolution
smbclient -L ip addr/hostname Display remote shares from a Windows host
smbget -Rr smb://ip addr/share Downloads files from a Windows host via SMB, akin to wget
Linux Commands — IPTABLES (Firewall)
Command Code Comment Description
iptables -t filter -L Display all chains in the filter table
iptables -t nat -L Corrected: Display all chains in the nat table
iptables -t filter -F Flush all rules based on the filter table
iptables -t nat -F Flush all rules based on the nat table
iptables -t filter -X Delete all links created by the user
iptables -t filter -A INPUT -p tcp --dport telnet -j ACCEPT Allow telnet access
iptables -t filter -A OUTPUT -p tcp --dport telnet -j DROP Block telnet access
iptables -t filter -A FORWARD -p tcp --dport pop3 -j ACCEPT Allow forwarding of POP3 connections on the link
iptables -t filter -A INPUT -j LOG --log-prefix Log all packets that are blocked in the link
iptables -t nat -A POSTROUTING -o eth -j MASQUERADE Set up a PAT (Port Address Translation) on eth to mask outgoing packets
iptables -t nat -A POSTROUTING -d 192.168..1 -p tcp -m tcp --dport 22 -j DNAT --to-destination 10...2:22 Redirect packets sent to a host address to another host
Linux Commands — Monitoring and Debugging
Command Code Comment Description
free -m List RAM status in megabytes
kill -9 process id Forcefully close a process and end it
kill -1 process id Force a process to reload its configuration
last reboot Display reboot history
lsmod List loaded kernel modules
lsof -p process id List a file list opened by a process
lsof /home/user1 List the list of files opened in the given system path
ps -eafw List Linux tasks
ps -e -o pid,args --forest List Linux tasks in a hierarchical manner
pstress Display programs in a tree diagram
smartctl -A /dev/hda Monitor the reliability of a hard disk device by enabling SMART
smartctl -i /dev/hda Check whether the SMART of a hard disk device is enabled
strace -c ls >/dev/null List system calls made and receive them with a process
strace -f -e open ls >/dev/null List library calls
tail /var/log/dmesg Display internal events during the kernel boot process
tail /val/log/messages Display system events
top List Linux tasks that use the most CPU resources
watch -nl ‘cat /proc/interrupts’ List real-time interrupts
Linux Commands — Other Common Commands
Command Code Comment Description
alias hh='history' Set an alias for the history command
apropos ...keyword List a command list including the program keyword, especially useful when you only know what the program does and do not remember the command
chsh Change the shell command
chsh --list-shells A good command to know if you need to remotely connect to another machine
gpg -c filel Encrypt a file with GNU Privacy Guard
gpg filel.gpg Decrypt a file with GNU Privacy Guard
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