A complete list of commonly used Linux commands,Tips: Ctrl+F to quickly find Linux commands (click the title to shrink or expand)
| command code | Notes |
|---|---|
| arch | Shows the machine's processor architecture (1) |
| uname -m | Shows the machine's processor architecture (2) |
| uname -r | Show the kernel version in use |
| dmidecode -q | Display hardware system components - (SMBIOS/DMI) |
| hdparm -i /dev/hda | List the architectural features of a disk |
| hdparm -tT /dev/sda | Perform a test read operation on disk |
| cat /proc/cpuinfo | Display CPU info information |
| cat /proc/interrupts | Display interruption |
| cat /proc/meminfo | Verify memory usage |
| cat /proc/swaps | Show which swaps are used |
| cat /proc/version | Show kernel version |
| cat /proc/net/dev | Show network adapters and statistics |
| cat /proc/mounts | Show mounted file systems |
| lspci -tv | List PCI devices |
| lsusb -tv | Show USB devices |
| date | Show system date |
| cal 2007 | Show calendar for 2007 |
| date 041217002007.00 | Set date and time - month, day, hour, minute, year, second |
| clock -w | Save time modifications to BIOS |
| command code | Notes |
|---|---|
| shutdown -h now | Shut down the system |
| init 0 | Shut down the system |
| telinit 0 | Shut down the system |
| shutdown -h hours:minutes & | Shut down the system at a scheduled time |
| shutdown -c | Cancel a scheduled system shutdown |
| shutdown -r now | Restart |
| reboot | Restart |
| logout | Log out |
| command code | Notes |
|---|---|
| cd /home | Enter the '/home' directory' |
| cd .. | Return to the previous directory |
| cd ../.. | Return to the previous two levels of directory |
| cd | Enter your personal home directory |
| cd ~user1 | Enter your personal home directory |
| cd - | Return to the last directory |
| pwd | show working path |
| ls | View files in a directory |
| ls -F | View files in a directory |
| ls -l | Show file and directory details |
| ls -a | Show hidden files |
| ls *[0-9]* | Display file and directory names containing numbers |
| tree | Displays a tree structure of files and directories starting from the root directory |
| lstree | Displays a tree structure of files and directories starting from the root directory |
| mkdir dir1 | Create a directory called 'dir1' |
| mkdir dir1 dir2 | Create two directories at the same time |
| mkdir -p /tmp/dir1/dir2 | Create a directory tree |
| rm -f file1 | Delete a file called 'file1' |
| rmdir dir1 | Delete a directory called 'dir1' |
| rm -rf dir1 | Delete a directory called 'dir1' and delete its contents as well |
| rm -rf dir1 dir2 | Delete both directories and their contents simultaneously |
| mv dir1 new_dir | Rename/move a directory |
| cp file1 file2 | copy a file |
| cp dir/* . | Copy all files in 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 soft link to a file or directory |
| ln file1 lnk1 | Create a physical link to a file or directory |
| touch -t 0712250000 file1 | Modify the timestamp of a file or directory - (YYMMDDhhmm) |
| iconv -l | List known encodings |
| iconv -f fromEncoding -t toEncoding inputFile > outputFile | Change character encoding |
| find . -maxdepth 1 -name *.jpg -print -exec convert | Batch resize files in current directory and send them to thumbnail directory (requires conversion from ImageMagick) |
| command code | Notes |
|---|---|
| find / -name file1 | Search for files and directories in the root file system starting from '/' |
| find / -user user1 | Search files and directories belonging to user 'user1' |
| find /home/user1 -name \*.bin | Search the directory '/home/user1' for files ending with '.bin' |
| 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 created or modified within 10 days |
| find / -name \*.rpm -exec chmod 755 '{}' \; | Search for files ending with '.rpm' and define their permissions |
| find / -xdev -name \*.rpm | Search for files ending with '.rpm', ignoring removable devices such as CD-ROM drives and USB drives |
| locate \*.ps | Find files ending with '.ps' - run 'updatedb' command first |
| whereis halt | Display the location of a binary file, source code or man |
| which halt | Displays the full path to a binary or executable file |
| command code | Notes |
|---|---|
| mount /dev/hda2 /mnt/hda2 | Mount a disk called hda2 - make sure the directory '/mnt/hda2' already exists |
| umount /dev/hda2 | Unmount a disk called hda2 - Exit from the mount point '/mnt/hda2' first |
| fuser -km /mnt/hda2 | Force uninstall when device is busy |
| umount -n /mnt/hda2 | Run an uninstall operation without writing to the /etc/mtab file - useful when the file is read-only or when the disk is full |
| mount /dev/fd0 /mnt/floppy | Mount a floppy disk |
| mount /dev/cdrom /mnt/cdrom | Mount a cdrom or dvdrom |
| mount /dev/hdc /mnt/cdrecorder | Mount a cdrw or dvdrom |
| mount /dev/hdb /mnt/cdrecorder | Mount a cdrw or dvdrom |
| 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 |
| command code | Notes |
|---|---|
| df -h | Display the list of mounted partitions |
| ls -lSr |more | Arrange files and directories by size |
| du -sh dir1 | Estimated disk space used by directory 'dir1' |
| du -sk * | sort -rn | Display the size of files and directories in sequence based on capacity |
| rpm -q -a --qf '%10{SIZE}t%{NAME}n' | sort -k1,1n | Display the space used by installed rpm packages based on size (fedora, redhat type systems) |
| dpkg-query -W -f='${Installed-Size;10}t${Package}n' | sort -k1,1n | Display the space used by installed deb packages based on size (ubuntu, debian system) |
| command code | Notes |
|---|---|
| groupadd group_name | Create a new user group |
| groupdel group_name | Delete a user group |
| groupmod -n new_group_name old_group_name | Rename a user group |
| useradd -c "Name Surname " -g admin -d /home/user1 -s /bin/bash user1 | Create a user belonging to the "admin" user group |
| useradd user1 | Create a new user |
| userdel -r user1 | Remove a user ('-r' excludes home directory) |
| usermod -c "User FTP" -g system -d /ftp/user1 -s /bin/nologin user1 | Modify user attributes |
| passwd | Change password |
| passwd user1 | Modify a user's password (only allowed to be executed by root) |
| chage -E 2020-12-31 user1 | Set user password expiration date |
| pwck | Check '/etc/passwd' for file format and syntax fixes and existing users |
| grpck | Check '/etc/passwd' for file format and syntax fixes and existing groups |
| newgrp group_name | Log into a new group to change the default group for newly created files |
| command code | Notes |
|---|---|
| ls -lh | Show permissions |
| ls /tmp | pr -T5 -W$COLUMNS | Divide the terminal into 5 columns for display |
| chmod ugo+rwx directory1 | Set the directory owner (u), group (g) and others (o) to read (r), write (w) and execute (x) permissions |
| chmod go-rwx directory1 | Remove the read, write, and execute permissions of the group (g) and others (o) on the directory |
| chown user1 file1 | Change the owner attribute of a file |
| chown -R user1 directory1 | Change the owner attributes of a directory and simultaneously change the attributes of all files in the directory |
| chgrp group1 file1 | Change the group of a file |
| chown user1:group1 file1 | Change the owner and group attributes of a file |
| find / -perm -u+s | List all files controlled by SUID in a system |
| chmod u+s /bin/file1 | Set the SUID bit of a binary file - the user running the file is also given the same permissions as the owner |
| chmod u-s /bin/file1 | Disable the SUID bit of a binary file |
| chmod g+s /home/public | Sets the SGID bit of 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 on a file - only allows the legitimate owner to delete the file |
| chmod o-t /home/public | Disable the STIKY bit for a directory |
| command code | Notes |
|---|---|
| chattr +a file1 | Only allowed to read and write files in append mode |
| chattr +c file1 | Allow this file to be automatically compressed/decompressed by the kernel |
| chattr +d file1 | The dump program will ignore this file when doing a file system backup |
| chattr +i file1 | Files set to be immutable cannot be deleted, modified, renamed or linked to |
| chattr +s file1 | Allow a file to be safely deleted |
| chattr +S file1 | Once the application performs a write operation on this file, the system immediately writes the modified results to the disk. |
| chattr +u file1 | If a file is deleted, the system will allow you to recover the deleted file later |
| lsattr | Show special properties |
| command code | Notes |
|---|---|
| bunzip2 file1.bz2 | Unzip a file called 'file1.bz2' |
| bzip2 file1 | Compress a file called 'file1' |
| gunzip file1.gz | Unzip a file called 'file1.gz' |
| gzip file1 | Compress 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 | Compress 'file1', 'file2' and 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 compressed package in bzip2 format |
| tar -jxvf archive.tar.bz2 | Decompress a compressed package in bzip2 format |
| tar -cvfz archive.tar.gz dir1 | Create a compressed package in gzip format |
| tar -zxvf archive.tar.gz | Decompress a compressed package in gzip format |
| zip file1.zip file1 | Create a compressed package in zip format |
| zip -r file1.zip file1 file2 dir1 | Compress several files and directories into a compressed package in zip format at the same time |
| unzip file1.zip | Unzip a zip format compressed package |
| command code | Notes |
|---|---|
| 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 changing its configuration file |
| rpm -F package.rpm | Update an rpm package that is already installed |
| rpm -e package_name.rpm | Delete 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 name |
| rpm -qi package_name | Get special information about an installed package |
| rpm -qg "System Environment/Daemons" | Display the rpm package of a component |
| rpm -ql package_name | Display a list of files provided by an installed rpm package |
| rpm -qc package_name | Display a list of configuration files provided by an installed rpm package |
| rpm -q package_name --whatrequires | Display a list of dependencies on an rpm package |
| rpm -q package_name --whatprovides | Display the volume occupied by an rpm package |
| rpm -q package_name --scripts | Show scripts executed during installation/removal |
| rpm -q package_name --changelog | Display the modification history of an rpm package |
| rpm -qf /etc/httpd/conf/httpd.conf | Confirm which rpm package the given file is provided by |
| rpm -qp package.rpm -l | Display a list of files provided by an rpm package that has not yet been installed |
| rpm --import /media/cdrom/RPM-GPG-KEY | Import 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, permission, type, owner, group, MD5 check and last modified time |
| rpm -Va | Check all installed rpm packages on the system - use with caution |
| rpm -Vp package.rpm | Confirm that an rpm package has not been installed yet |
| rpm2cpio package.rpm | cpio --extract --make-directories *bin* | Run an executable file 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 an rpm source code |
| command code | Notes |
|---|---|
| yum install package_name | Download and install an rpm package |
| yum localinstall package_name.rpm | will install an rpm package, using your own software repository to resolve all dependencies for you |
| yum update package_name.rpm | Update all rpm packages installed 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 installed on the current system |
| yum search package_name | Search for packages in the rpm repository |
| yum clean packages | Clean rpm cache and delete downloaded packages |
| yum clean headers | Remove all header files |
| yum clean all | Remove all cached packages and header files |
| command code | Notes |
|---|---|
| dpkg -i package.deb | Install/update a deb package |
| dpkg -r package_name | Remove a deb package from the system |
| dpkg -l | Display all installed deb packages in the system |
| dpkg -l | grep httpd | Display all deb packages with "httpd" in their name |
| dpkg -s package_name | Get information about a particular package that has been installed on the system |
| dpkg -L package_name | Display the file list provided by a deb package that has been installed on the system |
| dpkg --contents package.deb | Displays a list of files provided by a package that is not yet installed |
| dpkg -S /bin/ping | Confirm which deb package the given file is provided by |
| command code | Notes |
|---|---|
| apt-get install package_name | Install/update a deb package |
| apt-cdrom install package_name | Install/update a deb package from CD |
| apt-get update | Upgrade packages in list |
| apt-get upgrade | Upgrade all installed software |
| apt-get remove package_name | Delete a deb package from the system |
| apt-get check | Confirm that the dependent software repository is correct |
| apt-get clean | Clean cache from downloaded packages |
| apt-cache search searched-package | Returns the package name containing the search string |
| command code | Notes |
|---|---|
| cat file1 | View the contents of the file forward starting from the first byte |
| tac file1 | View the contents of a file in reverse order starting 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 on files as well as 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 | View content being added to a file in real time |
| command code | Notes |
|---|---|
| cat file1 | command( sed, grep, awk, grep, etc...) > result.txt | Merge the detailed description text of one file and write the introduction to a new file |
| cat file1 | command( sed, grep, awk, grep, etc...) >> result.txt | Merge the detailed description text of a file and write the introduction to an existing file |
| grep Aug /var/log/messages | Search for the keyword "Aug" in the file '/var/log/messages' |
| grep ^Aug /var/log/messages | Search the file '/var/log/messages' for words starting with "Aug" |
| grep [0-9] /var/log/messages | Select all lines containing numbers in the '/var/log/messages' file |
| grep Aug -R /var/log/* | Search the directory '/var/log' and subsequent directories for the string "Aug" |
| sed 's/stringa1/stringa2/g' example.txt | Replace "string1" in the example.txt file with "string2" |
| sed '/^$/d' example.txt | Remove all blank lines from example.txt file |
| sed '/ *#/d; /^$/d' example.txt 从example.txt | Remove all comments and blank lines from the file |
| echo 'esempio' | tr '[:lower:]' '[:upper:]' | Merge the contents of upper and lower cells |
| sed -e '1d' result.txt | Exclude the first line from the file example.txt |
| sed -n '/stringa1/p' | View lines containing only the word "string1" |
| sed -e 's/ *$//' example.txt | Remove whitespace characters at the end of each line |
| sed -e 's/stringa1//g' example.txt | Remove only the word "string1" from the document and keep everything else |
| sed -n '1,5p;5q' example.txt | View content from line 1 to line 5 |
| sed -n '5p;5q' example.txt | Look at line 5 |
| sed -e 's/00*/0/g' example.txt | Replace multiple zeros with a single zero |
| cat -n file1 | Indicates the number of lines in the file |
| cat example.txt | awk 'NR%2==1' | Delete all even lines in example.txt file |
| echo a b c | awk '{print $1}' | View the first column of a row |
| echo a b c | awk '{print $1,$3}' | Look at the first and third columns of a row |
| paste file1 file2 | Merge the contents of two files or columns |
| paste -d '+' file1 file2 | Merge the contents of two files or two columns, using "+" to distinguish them. |
| sort file1 file2 | Sort the contents of two files |
| sort file1 file2 | uniq | Take the union of two files (only one copy of duplicate lines is kept) |
| sort file1 file2 | uniq -u | Remove intersection, leaving other rows |
| sort file1 file2 | uniq -d | Take out the intersection of two files (leaving only files that exist in both files) |
| comm -1 file1 file2 | Compare the contents of two files and delete only the contents contained in 'file1' |
| comm -2 file1 file2 | Compare the contents of two files and delete only the contents contained in 'file2' |
| comm -3 file1 file2 | Compare the contents of two files and delete only the parts common to both files |
| command code | Notes |
|---|---|
| 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 | Show all allowed conversion formats |
| command code | Notes |
|---|---|
| badblocks -v /dev/hda1 | Check for bad blocks on disk hda1 |
| fsck /dev/hda1 | Repair/check integrity of linux file system on hda1 disk |
| fsck.ext2 /dev/hda1 | Repair/check integrity of ext2 file system on hda1 disk |
| e2fsck /dev/hda1 | Repair/check integrity of ext2 file system on hda1 disk |
| e2fsck -j /dev/hda1 | Repair/check integrity of ext3 file system on hda1 disk |
| fsck.ext3 /dev/hda1 | Repair/check integrity of ext3 file system on hda1 disk |
| fsck.vfat /dev/hda1 | Repair/check integrity of fat file system on hda1 disk |
| fsck.msdos /dev/hda1 | Repair/check integrity of dos file system on hda1 disk |
| dosfsck /dev/hda1 | Repair/check integrity of dos file system on hda1 disk |
| command code | Notes |
|---|---|
| mkfs /dev/hda1 | Create a file system on the hda1 partition |
| mke2fs /dev/hda1 | Create a linux ext2 file system on the hda1 partition |
| mke2fs -j /dev/hda1 | Create a linux ext3 (journaled) file system in the hda1 partition |
| mkfs -t vfat 32 -F /dev/hda1 | Create a FAT32 file system |
| fdformat -n /dev/fd0 | Format a floppy disk |
| mkswap /dev/hda3 | Create a swap file system |
| command code | Notes |
|---|---|
| mkswap /dev/hda3 | Create a swap file system |
| swapon /dev/hda3 | Enable a new swap file system |
| swapon /dev/hda2 /dev/hdb3 | Enable two swap partitions |
| command code | Notes |
|---|---|
| dump -0aj -f /tmp/home0.bak /home | Make a full backup of the '/home' directory |
| dump -1aj -f /tmp/home0.bak /home | Make an interactive backup of the '/home' directory |
| restore -if /tmp/home0.bak | Restoring an interactive backup |
| rsync -rogpav --delete /home /tmp | Synchronize directories on both sides |
| rsync -rogpav -e ssh --delete /home ip_address:/tmp | rsync over SSH channel |
| rsync -az -e ssh --delete ip_addr:/home/public /home/local | Sync a remote directory to a local directory via ssh and compression |
| rsync -az -e ssh --delete /home/local ip_addr:/home/public | Sync local directory to remote directory via ssh and compression |
| dd bs=1M if=/dev/hda | gzip | ssh user@ip_addr 'dd of=hda.gz' | Perform a local disk backup operation on the remote host through ssh |
| dd if=/dev/sda of=/tmp/file1 | Back up disk contents to a file |
| tar -Puf backup.tar /home/user | Perform an interactive backup of the '/home/user' directory |
| ( cd /tmp/local/ && tar c . ) | ssh -C user@ip_addr 'cd /home/share/ && tar x -p' | Copy the contents of a directory to a remote directory via ssh |
| ( tar c /home ) | ssh -C user@ip_addr 'cd /home/backup-home && tar x -p' | Copy a local directory in a remote directory via ssh |
| tar cf - . | (cd /tmp/backup ; tar xf - ) | Copy a directory locally to another place, retaining original permissions and links |
| find /home/user1 -name '*.txt' | xargs cp -av --target-directory=/home/backup/ --parents | Find and copy all files ending with '.txt' from one directory to another |
| find /var/log -name '*.log' | tar cv --files-from=- | bzip2 > log.tar.bz2 | Find all files ending with '.log' and make a bzip package |
| dd if=/dev/hda of=/dev/fd0 bs=512 count=1 | Perform an action to copy the contents of MBR (Master Boot Record) to a floppy disk |
| dd if=/dev/fd0 of=/dev/hda bs=512 count=1 | Recover MBR contents from backup that has been saved to floppy disk |
| command code | Notes |
|---|---|
| cdrecord -v gracetime=2 dev=/dev/cdrom -eject blank=fast -force | Erase the contents of a rewritable disc |
| mkisofs /dev/cdrom > cd.iso | Create an iso image file of the CD on the disk |
| mkisofs /dev/cdrom | gzip > cd_iso.gz | Create a compressed CD iso image file 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 | Rip audio tracks from a CD to wav files |
| cd-paranoia -- "-3" | Rip audio tracks from a CD to a wav file (parameter -3) |
| cdrecord --scanbus | Scan bus to identify scsi channel |
| dd if=/dev/hdc | md5sum | Verify the md5sum encoding of a device, such as a CD |
| command code | Notes |
|---|---|
| dhclient eth0 | Enable 'eth0' network device in dhcp mode |
| ethtool eth0 | Display traffic statistics of network card 'eth0' |
| host www.example.com | Find hostnames to resolve names and IP addresses and mirrors |
| hostname | show hostname |
| ifconfig eth0 | Display the configuration of an Ethernet card |
| ifconfig eth0 192.168.1.1 netmask 255.255.255.0 | Control IP address |
| ifconfig eth0 promisc | Set 'eth0' to promiscuous mode to sniff packets (sniffing) |
| ifdown eth0 | Disable an 'eth0' network device |
| ifup eth0 | Enable an 'eth0' 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 | Show wireless networks |
| mii-tool eth0 | Show connection status of 'eth0' |
| netstat -tup | Show all enabled network connections and their PIDs |
| netstat -tup1 | Display all listening network services in the system and their PIDs |
| netstat -rn | Display the routing table, similar to the "route -n" command |
| nslookup www.example.com | Find hostnames to resolve names and IP addresses and mirrors |
| route -n | show routing table |
| route add -net 0/0 gw IP Gateway | Control default gateway |
| route add -net 192.168.0.0 netmask 255.255.0.0 gw 192.168.1.1 | Control static route to network '192.168.0.0/16' |
| route del 0/0 gw IP gateway | Delete static route |
| echo “1”> /proc/sys/net/ipv4/ip_foward | Activate IP forwarding |
| tcpdump tcp port 80 | Show all HTTP loopbacks |
| whois www.example.com | Search in Whois database |
| command code | Notes |
|---|---|
| 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 of a windows host |
| smbget -Rr smb://ip addr/share | Like wget, you can download files from a windows host via smb |
| command code | Notes |
|---|---|
| iptables -t filter -L | Show all links in the filter table |
| iptables -t nae -L | Display all links in the nat table |
| iptables -t filter -F | Clean up all rules based on filter table |
| iptables -t nat -F | Clean up all rules based on 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 POP3 connections on forwarding links |
| iptables -t filter -A INPUT -j LOG --log-prefix | Record blocked packets on all links |
| iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE | Set up a PAT (Port Address Translation) on eth0 to mask outgoing packets |
| iptables -t nat -A POSTROUTING -d 192.168.0.1 -p tcp -m tcp --dport 22-j DNAT --to-destination 10.0.0.2:22 | Forward packets destined for one host address to other hosts |
| command code | Notes |
|---|---|
| free -m | List RAM status in megabytes |
| kill -9 process id | Force close the process and end it |
| kill -1 process id | Force a process to reload its configuration |
| last reboot | Show restart history |
| lsmod | Kernel module that lists status |
| lsof -p process id | List a list of files opened by a process |
| lsof /home/user1 | List of open files 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 program in tree view |
| smartctl -A /dev/hda | Monitor the reliability of hard drive devices by enabling SMART |
| smartctl -i /dev/hda | Check whether SMART is enabled on a hard disk device |
| 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 kernel boot process |
| tail /val/log/messages | Show system events |
| top | List the Linux tasks that use the most CPU resources |
| watch -nl ‘cat /proc/interrupts’ | List real-time interrupts |
| command code | Notes |
|---|---|
| alias hh='history' | Set an alias for the command history |
| apropos ...keyword | Make a list of commands including program keywords. This is especially useful when you only know what the program does but don’t remember the commands. |
| chsh | Change shell command |
| chsh --list-shells | Nice command to know if you have to connect remotely to another machine |
| gpg -c filel | Encrypt a file with GNU Privacy Guard |
| gpg filel.gpg | Decrypt a file with GNU Privacy Guard |