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Version
Linux Command Line
version 1.4
Last modified date: 2009-07-03
Created Date: 2008-01-06
 
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Linux Command Line in English



|  System information  | Shutdown, Restart and Logout of a system  | Files and Directory  | File search  | Mounting a Filesystem  | Disk Space  | Users and Groups  | Permits on Files  | Special Attributes on files  | Archives and compressed files  | RPM Packages ( Fedora, Red Hat and like)  | YUM packages tool (Fedora, RedHat and alike)  | DEB packages (Debian, Ubuntu and like)  | APT packages tool (Debian, Ubuntu and alike)  | View file content  | Text Manipulation  | Character set and Format file conversion  | Filesystem Analysis  | Format a Filesystem  | Filesystem SWAP  | Backup  | CDROM  | Networking (LAN / WiFi)  | Microsoft Windows networks (samba)  | IPTABLES (firewall)  | Monitoring and debugging  | Other useful commands  | Pacman packages tool (Arch, Frugalware and alike)  |

System information

Command Description
# arch show architecture of machine(1)   [man]
# cal 2007 show the timetable of 2007   [man]
# cat /proc/cpuinfo show information CPU info   [man]
# cat /proc/interrupts show interrupts   [man]
# cat /proc/meminfo verify memory use   [man]
# cat /proc/swaps show file(s) swap   [man]
# cat /proc/version show version of the kernel   [man]
# cat /proc/net/dev show network adpters and statistics   [man]
# cat /proc/mounts show mounted file system(s)   [man]
# clock -w save date changes on BIOS   [man]
# date show system date   [man]
# date 041217002007.00 set date and time - MonthDayhoursMinutesYear.Seconds   [man]
# dmidecode -q show hardware system components - (SMBIOS / DMI)   [man]
# hdparm -i /dev/hda displays the characteristics of a hard-disk   [man]
# hdparm -tT /dev/sda perform test reading on a hard-disk   [man]
# lspci -tv display PCI devices   [man]
# lsusb -tv show USB devices   [man]
# uname -m show architecture of machine(2)   [man]
# uname -r show used kernel version   [man]
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Shutdown, Restart and Logout of a system

Command Description
# init 0 shutdown system(2)   [man]
# logout leaving session   [man]
# reboot reboot(2)   [man]
# shutdown -h now shutdown system(1)   [man]
# shutdown -h 16:30 & planned shutdown of the system   [man]
# shutdown -c cancel a planned shutdown of the system   [man]
# shutdown -r now reboot(1)   [man]
# telinit 0 shutdown system(3)   [man]
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Files and Directory

Command Description
# cd /home enter to directory '/ home'   [man]
# cd .. go back one level   [man]
# cd ../.. go back two levels   [man]
# cd go to home directory   [man]
# cd ~user1 go to home directory   [man]
# cd - go to previous directory   [man]
# cp file1 file2 copying a file   [man]
# cp dir/* . copy all files of a directory within the current work directory   [man]
# cp -a /tmp/dir1 . copy a directory within the current work directory   [man]
# cp -a dir1 dir2 copy a directory   [man]
# cp file file1 outputs the mime type of the file as text   [man]
# iconv -l lists known encodings   [man]
# iconv -f fromEncoding -t toEncoding inputFile > outputFile converting the coding of characters from one format to another   [man]
# find . -maxdepth 1 -name *.jpg -print -exec convert batch resize files in the current directory and send them to a thumbnails directory (requires convert from Imagemagick)   [man]
# ln -s file1 lnk1 create a symbolic link to file or directory   [man]
# ln file1 lnk1 create a physical link to file or directory   [man]
# ls view files of directory   [man]
# ls -F view files of directory   [man]
# ls -l show details of files and directory   [man]
# ls -a show hidden files   [man]
# ls *[0-9]* show files and directory containing numbers   [man]
# lstree show files and directories in a tree starting from root(2)   [man]
# mkdir dir1 create a directory called 'dir1'   [man]
# mkdir dir1 dir2 create two directories simultaneously   [man]
# mkdir -p /tmp/dir1/dir2 create a directory tree   [man]
# mv dir1 new_dir rename / move a file or directory   [man]
# pwd show the path of work directory   [man]
# rm -f file1 delete file called 'file1'   [man]
# rm -rf dir1 remove a directory called 'dir1' and contents recursively   [man]
# rm -rf dir1 dir2 remove two directories and their contents recursively   [man]
# rmdir dir1 delete directory called 'dir1'   [man]
# touch -t 0712250000 file1 modify timestamp of a file or directory - (YYMMDDhhmm)   [man]
# tree show files and directories in a tree starting from root(1)   [man]
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File search

Command Description
# find / -name file1 search file and directory into root filesystem from '/'   [man]
# find / -user user1 search files and directories belonging to 'user1'   [man]
# find /home/user1 -name \*.bin search files with '. bin' extension within directory '/ home/user1'   [man]
# find /usr/bin -type f -atime +100 search binary files are not used in the last 100 days   [man]
# find /usr/bin -type f -mtime -10 search files created or changed within 10 days   [man]
# find / -name *.rpm -exec chmod 755 '{}' \; search files with '.rpm' extension and modify permits   [man]
# find / -xdev -name \*.rpm search files with '.rpm' extension ignoring removable partitions as cdrom, pen-drive, etc.…   [man]
# locate \*.ps find files with the '.ps' extension - first run 'updatedb' command   [man]
# whereis halt show location of a binary file, source or man   [man]
# which halt show full path to a binary / executable   [man]
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Mounting a Filesystem

Command Description
# fuser -km /mnt/hda2 force umount when the device is busy   [man]
# mount /dev/hda2 /mnt/hda2 mount disk called hda2 - verify existence of the directory '/ mnt/hda2'   [man]
# mount /dev/fd0 /mnt/floppy mount a floppy disk   [man]
# mount /dev/cdrom /mnt/cdrom mount a cdrom / dvdrom   [man]
# mount /dev/hdc /mnt/cdrecorder mount a cdrw / dvdrom   [man]
# mount /dev/hdb /mnt/cdrecorder mount a cdrw / dvdrom   [man]
# mount -o loop file.iso /mnt/cdrom mount a file or iso image   [man]
# mount -t vfat /dev/hda5 /mnt/hda5 mount a Windows FAT32 file system   [man]
# mount /dev/sda1 /mnt/usbdisk mount a usb pen-drive or flash-drive   [man]
# mount -t smbfs -o username=user,password=pass //WinClient/share /mnt/share mount a windows network share   [man]
# umount /dev/hda2 unmount disk called hda2 - exit from mount point '/ mnt/hda2' first   [man]
# umount -n /mnt/hda2 run umount without writing the file /etc/mtab - useful when the file is read-only or the hard disk is full   [man]
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Disk Space

Command Description
# df -h show list of partitions mounted   [man]
# dpkg-query -W -f='${Installed-Size;10}t${Package}n' | sort -k1,1n show the used space by installed deb packages, sorting by size (debian, ubuntu and alike)   [man]
# du -sh dir1 estimate space used by directory 'dir1'   [man]
# du -sk * | sort -rn show size of the files and directories sorted by size   [man]
# ls -lSr |more show size of the files and directories ordered by size   [man]
# rpm -q -a --qf '%10{SIZE}t%{NAME}n' | sort -k1,1n show space used by rpm packages installed sorted by size (fedora, redhat and like)   [man]
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Users and Groups

Command Description
# chage -E 2005-12-31 user1 set deadline for user password   [man]
# groupadd [group] create a new group   [man]
# groupdel [group] delete a group   [man]
# groupmod -n moon sun rename a group from moon to sun   [man]
# grpck check correct syntax and file format of '/etc/group' and groups existence   [man]
# newgrp - [group] log into a new group to change default group of newly created files   [man]
# passwd change password   [man]
# passwd user1 change a user password (only by root)   [man]
# pwck check correct syntax and file format of '/etc/passwd' and users existence   [man]
# useradd -c "User Linux" -g admin -d /home/user1 -s /bin/bash user1 create a new user "user1" belongs "admin" group   [man]
# useradd user1 create a new user   [man]
# userdel -r user1 delete a user ( '-r' eliminates home directory)   [man]
# usermod -c "User FTP" -g system -d /ftp/user1 -s /bin/nologin user1 change user attributes   [man]
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Permits on Files

Command Description
# chgrp group1 file1 change group of files   [man]
# chmod ugo+rwx directory1 set permissions reading (r), write (w) and (x) access to users owner (u) group (g) and others (o)   [man]
# chmod go-rwx directory1 remove permits reading (r), write (w) and (x) access to users group (g) and others (or   [man]
# chmod u+s /bin/file1 set SUID bit on a binary file - the user that running that file gets same privileges as owner   [man]
# chmod u-s /bin/file1 disable SUID bit on a binary file   [man]
# chmod g+s /home/public set SGID bit on a directory - similar to SUID but for directory   [man]
# chmod g-s /home/public disable SGID bit on a directory   [man]
# chmod o+t /home/public set STIKY bit on a directory - allows files deletion only to legitimate owners   [man]
# chmod o-t /home/public disable STIKY bit on a directory   [man]
# chown user1 file1 change owner of a file   [man]
# chown -R user1 directory1 change user owner of a directory and all the files and directories contained inside   [man]
# chown user1:group1 file1 change user and group ownership of a file   [man]
# find / -perm -u+s view all files on the system with SUID configured   [man]
# ls -lh show permits on files   [man]
# ls /tmp | pr -T5 -W$COLUMNS divide terminal into 5 columns   [man]
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Special Attributes on files

Command Description
# chattr +a file1 allows write opening of a file only append mode   [man]
# chattr +c file1 allows that a file is compressed / decompressed automatically by the kernel   [man]
# chattr +d file1 makes sure that the program ignores Dump the files during backup   [man]
# chattr +i file1 makes it an immutable file, which can not be removed, altered, renamed or linked   [man]
# chattr +s file1 allows a file to be deleted safely   [man]
# chattr +S file1 makes sure that if a file is modified changes are written in synchronous mode as with sync   [man]
# chattr +u file1 allows you to recover the contents of a file even if it is canceled   [man]
# lsattr show specials attributes   [man]
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Archives and compressed files

Command Description
# bunzip2 file1.bz2 decompress a file called 'file1.bz2'   [man]
# bzip2 file1 compress a file called 'file1'   [man]
# gunzip file1.gz decompress a file called 'file1.gz'   [man]
# gzip file1 compress a file called 'file1'   [man]
# gzip -9 file1 compress with maximum compression   [man]
# rar a file1.rar test_file create an archive rar called 'file1.rar'   [man]
# rar a file1.rar file1 file2 dir1 compress 'file1', 'file2' and 'dir1' simultaneously   [man]
# rar x file1.rar decompress rar archive   [man]
# tar -cvf archive.tar file1 create a uncompressed tarball   [man]
# tar -cvf archive.tar file1 file2 dir1 create an archive containing 'file1', 'file2' and 'dir1'   [man]
# tar -tf archive.tar show contents of an archive   [man]
# tar -xvf archive.tar extract a tarball   [man]
# tar -xvf archive.tar -C /tmp extract a tarball into / tmp   [man]
# tar -cvfj archive.tar.bz2 dir1 create a tarball compressed into bzip2   [man]
# tar -xvfj archive.tar.bz2 decompress a compressed tar archive in bzip2   [man]
# tar -cvfz archive.tar.gz dir1 create a tarball compressed into gzip   [man]
# tar -xvfz archive.tar.gz decompress a compressed tar archive in gzip   [man]
# unrar x file1.rar decompress rar archive   [man]
# unzip file1.zip decompress a zip archive   [man]
# zip file1.zip file1 create an archive compressed in zip   [man]
# zip -r file1.zip file1 file2 dir1 compress in zip several files and directories simultaneously   [man]
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RPM Packages ( Fedora, Red Hat and like)

Command Description
# rpm -ivh [package.rpm] install a rpm package   [man]
# rpm -ivh --nodeeps [package.rpm] install a rpm package ignoring dependencies requests   [man]
# rpm -U [package.rpm] upgrade a rpm package without changing configuration files   [man]
# rpm -F [package.rpm] upgrade a rpm package only if it is already installed   [man]
# rpm -e [package] remove a rpm package   [man]
# rpm -qa show all rpm packages installed on the system   [man]
# rpm -qa | grep httpd show all rpm packages with the name "httpd"   [man]
# rpm -qi [package] obtain information on a specific package installed   [man]
# rpm -qg "System Environment/Daemons" show rpm packages of a group software   [man]
# rpm -ql [package] show list of files provided by a rpm package installed   [man]
# rpm -qc [package] show list of configuration files provided by a rpm package installed   [man]
# rpm -q [package] --whatrequires show list of dependencies required for a rpm packet   [man]
# rpm -q [package] --whatprovides show capability provided by a rpm package   [man]
# rpm -q [package] --scripts show scripts started during installation / removal   [man]
# rpm -q [package] --changelog show history of revisions of a rpm package   [man]
# rpm -qf /etc/httpd/conf/httpd.conf verify which rpm package belongs to a given file   [man]
# rpm -qp [package.rpm] -l show list of files provided by a rpm package not yet installed   [man]
# rpm --import /media/cdrom/RPM-GPG-KEY import public-key digital signature   [man]
# rpm --checksig [package.rpm] verify the integrity of a rpm package   [man]
# rpm -qa gpg-pubkey verify integrity of all rpm packages installed   [man]
# rpm -V [package] check file size, permissions, type, owner, group, MD5 checksum and last modification   [man]
# rpm -Va check all rpm packages installed on the system - use with caution   [man]
# rpm -Vp [package.rpm] verify a rpm package not yet installed   [man]
# rpm -ivh /usr/src/redhat/RPMS/`arch`/[package.rpm] install a package built from a rpm source   [man]
# rpm2cpio [package.rpm] | cpio --extract --make-directories *bin* extract executable file from a rpm package   [man]
# rpmbuild --rebuild [package.src.rpm] build a rpm package from a rpm source   [man]
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YUM packages tool (Fedora, RedHat and alike)

Command Description
# yum -y install [package] download and install a rpm package   [man]
# yum localinstall [package.rpm] That will install an RPM, and try to resolve all the dependencies for you using your repositories.   [man]
# yum -y update update all rpm packages installed on the system   [man]
# yum update [package] upgrade a rpm package   [man]
# yum remove [package] remove a rpm package   [man]
# yum list list all packages installed on the system   [man]
# yum search [package] find a package on rpm repository   [man]
# yum clean [package] clean up rpm cache erasing downloaded packages   [man]
# yum clean headers remove all files headers that the system uses to resolve dependency   [man]
# yum clean all remove from the cache packages and headers files   [man]
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DEB packages (Debian, Ubuntu and like)

Command Description
# dpkg -i [package.deb] install / upgrade a deb package   [man]
# dpkg -r [package] remove a deb package from the system   [man]
# dpkg -l show all deb packages installed on the system   [man]
# dpkg -l | grep httpd show all deb packages with the name "httpd"   [man]
# dpkg -s [package] obtain information on a specific package installed on system   [man]
# dpkg -L [package] show list of files provided by a package installed on system   [man]
# dpkg --contents [package.deb] show list of files provided by a package not yet installed   [man]
# dpkg -S /bin/ping verify which package belongs to a given file   [man]
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APT packages tool (Debian, Ubuntu and alike)

Command Description
# apt-cache search [package] returns list of packages which corresponds string "searched-packages"   [man]
# apt-cdrom install [package] install / upgrade a deb package from cdrom   [man]
# apt-get install [package] install / upgrade a deb package   [man]
# apt-get update update the package list   [man]
# apt-get upgrade upgrade all of the installed packages   [man]
# apt-get remove [package] remove a deb package from system   [man]
# apt-get check verify correct resolution of dependencies   [man]
# apt-get clean clean up cache from packages downloaded   [man]
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Pacman packages tool (Arch, Frugalware and alike)

Command Description
# pacman -S name Install package 'name' with dependencies   [man]
# pacman -R name Delete package 'name' and all files of it   [man]
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View file content

Command Description
# cat file1 view the contents of a file starting from the first row   [man]
# head -2 file1 view first two lines of a file   [man]
# less file1 similar to 'more' command but which allows backward movement in the file as well as forward movement   [man]
# more file1 view content of a file along   [man]
# tac file1 view the contents of a file starting from the last line   [man]
# tail -2 file1 view last two lines of a file   [man]
# tail -f /var/log/messages view in real time what is added to a file   [man]
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Text Manipulation

Command Description
# cat example.txt | awk 'NR%2==1' remove all even lines from example.txt   [man]
# echo a b c | awk '{print $1}' view the first column of a line   [man]
# echo a b c | awk '{print $1,$3}' view the first and third column of a line   [man]
# cat -n file1 number row of a file   [man]
# comm -1 file1 file2 compare contents of two files by deleting only unique lines from 'file1'   [man]
# comm -2 file1 file2 compare contents of two files by deleting only unique lines from 'file2'   [man]
# comm -3 file1 file2 compare contents of two files by deleting only the lines that appear on both files   [man]
# diff file1 file2 find differences between two files   [man]
# grep Aug /var/log/messages look up words "Aug" on file '/var/log/messages'   [man]
# grep ^Aug /var/log/messages look up words that begin with "Aug" on file '/var/log/messages'   [man]
# grep [0-9] /var/log/messages select from file '/var/log/messages' all lines that contain numbers   [man]
# grep Aug -R /var/log/* search string "Aug" at directory '/var/log' and below   [man]
# paste file1 file2 merging contents of two files for columns   [man]
# paste -d '+' file1 file2 merging contents of two files for columns with '+' delimiter on the center   [man]
# sdiff file1 file2 find differences between two files and merge interactively alike "diff"   [man]
# sed 's/string1/string2/g' example.txt replace "string1" with "string2" in example.txt   [man]
# sed '/^$/d' example.txt remove all blank lines from example.txt   [man]
# sed '/ *#/d; /^$/d' example.txt remove comments and blank lines from example.txt   [man]
# sed -e '1d' exampe.txt eliminates the first line from file example.txt   [man]
# sed -n '/string1/p' view only lines that contain the word "string1"   [man]
# sed -e 's/ *$//' example.txt remove empty characters at the end of each row   [man]
# sed -e 's/string1//g' example.txt remove only the word "string1" from text and leave intact all   [man]
# sed -n '1,5p' example.txt print from 1th to 5th row of example.txt   [man]
# sed -n '5p;5q' example.txt print row number 5 of example.txt   [man]
# sed -e 's/00*/0/g' example.txt replace more zeros with a single zero   [man]
# sort file1 file2 sort contents of two files   [man]
# sort file1 file2 | uniq sort contents of two files omitting lines repeated   [man]
# sort file1 file2 | uniq -u sort contents of two files by viewing only unique line   [man]
# sort file1 file2 | uniq -d sort contents of two files by viewing only duplicate line   [man]
# echo 'word' | tr '[:lower:]' '[:upper:]' convert from lower case in upper case   [man]
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Character set and Format file conversion

Command Description
# dos2unix filedos.txt fileunix.txt convert a text file format from MSDOS to UNIX   [man]
# recode ..HTML < page.txt > page.html convert a text file to html   [man]
# recode -l | more show all available formats conversion   [man]
# unix2dos fileunix.txt filedos.txt convert a text file format from UNIX to MSDOS   [man]
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Filesystem Analysis

Command Description
# badblocks -v /dev/hda1 check bad blocks on disk hda1   [man]
# dosfsck /dev/hda1 repair / check integrity of dos filesystems on disk hda1   [man]
# e2fsck /dev/hda1 repair / check integrity of ext2 filesystem on disk hda1   [man]
# e2fsck -j /dev/hda1 repair / check integrity of ext3 filesystem on disk hda1   [man]
# fsck /dev/hda1 repair / check integrity of linux filesystem on disk hda1   [man]
# fsck.ext2 /dev/hda1 repair / check integrity of ext2 filesystem on disk hda1   [man]
# fsck.ext3 /dev/hda1 repair / check integrity of ext3 filesystem on disk hda1   [man]
# fsck.vfat /dev/hda1 repair / check integrity of fat filesystem on disk hda1   [man]
# fsck.msdos /dev/hda1 repair / check integrity of dos filesystem on disk hda1   [man]
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Format a Filesystem

Command Description
# fdformat -n /dev/fd0 format a floppy disk   [man]
# mke2fs /dev/hda1 create a filesystem type linux ext2 on hda1 partition   [man]
# mke2fs -j /dev/hda1 create a filesystem type linux ext3 (journal) on hda1 partition   [man]
# mkfs /dev/hda1 create a filesystem type linux on hda1 partition   [man]
# mkfs -t vfat 32 -F /dev/hda1 create a FAT32 filesystem   [man]
# mkswap /dev/hda3 create a swap filesystem   [man]
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Filesystem SWAP

Command Description
# mkswap /dev/hda3 create a swap filesystem   [man]
# swapon /dev/hda3 activating a new swap partition   [man]
# swapon /dev/hda2 /dev/hdb3 activate two swap partitions   [man]
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Backup

Command Description
# find /var/log -name '*.log' | tar cv --files-from=- | bzip2 > log.tar.bz2 find all files with '.log' extention and make an bzip archive   [man]
# find /home/user1 -name '*.txt' | xargs cp -av --target-directory=/home/backup/ --parents find and copy all files with '.txt' extention from a directory to another   [man]
# dd bs=1M if=/dev/hda | gzip | ssh user@ip_addr 'dd of=hda.gz' make a backup of a local hard disk on remote host via ssh   [man]
# dd if=/dev/sda of=/tmp/file1 backup content of the harddrive to a file   [man]
# dd if=/dev/hda of=/dev/fd0 bs=512 count=1 make a copy of MBR (Master Boot Record) to floppy   [man]
# dd if=/dev/fd0 of=/dev/hda bs=512 count=1 restore MBR from backup copy saved to floppy   [man]
# dump -0aj -f /tmp/home0.bak /home make a full backup of directory '/home'   [man]
# dump -1aj -f /tmp/home0.bak /home make a incremental backup of directory '/home'   [man]
# restore -if /tmp/home0.bak restoring a backup interactively   [man]
# rsync -rogpav --delete /home /tmp synchronization between directories   [man]
# rsync -rogpav -e ssh --delete /home ip_address:/tmp rsync via SSH tunnel   [man]
# rsync -az -e ssh --delete ip_addr:/home/public /home/local synchronize a local directory with a remote directory via ssh and compression   [man]
# rsync -az -e ssh --delete /home/local ip_addr:/home/public synchronize a remote directory with a local directory via ssh and compression   [man]
# tar -Puf backup.tar /home/user make a incremental backup of directory '/home/user'   [man]
# ( cd /tmp/local/ && tar c . ) | ssh -C user@ip_addr 'cd /home/share/ && tar x -p' copy content of a directory on remote directory via ssh   [man]
# ( tar c /home ) | ssh -C user@ip_addr 'cd /home/backup-home && tar x -p' copy a local directory on remote directory via ssh   [man]
# tar cf - . | (cd /tmp/backup ; tar xf - ) local copy preserving permits and links from a directory to another   [man]
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CDROM

Command Description
# cd-paranoia -B rip audio tracks from a CD to wav files   [man]
# cd-paranoia -- rip first three audio tracks from a CD to wav files   [man]
# cdrecord -v gracetime=2 dev=/dev/cdrom -eject blank=fast -force clean a rewritable cdrom   [man]
# cdrecord -v dev=/dev/cdrom cd.iso burn an ISO image   [man]
# gzip -dc cd_iso.gz | cdrecord dev=/dev/cdrom - burn a compressed ISO image   [man]
# cdrecord --scanbus scan bus to identify the channel scsi   [man]
# dd if=/dev/hdc | md5sum perform an md5sum on a device, like a CD   [man]
# mkisofs /dev/cdrom > cd.iso create an iso image of cdrom on disk   [man]
# mkisofs /dev/cdrom | gzip > cd_iso.gz create a compressed iso image of cdrom on disk   [man]
# mkisofs -J -allow-leading-dots -R -V create an iso image of a directory   [man]
# mount -o loop cd.iso /mnt/iso mount an ISO image   [man]
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Networking (LAN / WiFi)

Command Description
# dhclient eth0 active interface 'eth0' in dhcp mode   [man]
# ethtool eth0 show network statistics of eth0   [man]
# host www.example.com lookup hostname to resolve name to ip address and viceversa   [man]
# hostname show hostname of system   [man]
# ifconfig eth0 show configuration of an ethernet network card   [man]
# ifconfig eth0 192.168.1.1 netmask 255.255.255.0 configure IP Address   [man]
# ifconfig eth0 promisc configure 'eth0' in promiscuous mode to gather packets (sniffing)   [man]
# ifdown eth0 disable an interface 'eth0'   [man]
# ifup eth0 activate an interface 'eth0'   [man]
# ip link show show link status of all network interfaces   [man]
# iwconfig eth1 show wireless networks   [man]
# iwlist scan wifi scanning to display the wireless connections available   [man]
# mii-tool eth0 show link status of 'eth0'   [man]
# netstat -tup show all active network connections and their PID   [man]
# netstat -tupl show all network services listening on the system and their PID   [man]
# netstat -rn show routing table alike "route -n"   [man]
# nslookup www.example.com lookup hostname to resolve name to ip address and viceversa   [man]
# route -n show routing table   [man]
# route add -net 0/0 gw IP_Gateway configure default gateway   [man]
# route add -net 192.168.0.0 netmask 255.255.0.0 gw 192.168.1.1 configure static route to reach network '192.168.0.0/16'   [man]
# route del 0/0 gw IP_gateway remove static route   [man]
# echo "1" > /proc/sys/net/ipv4/ip_forward activate ip routing   [man]
# tcpdump tcp port 80 show all HTTP traffic   [man]
# whois www.example.com lookup on Whois database   [man]
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Microsoft Windows networks (samba)

Command Description
# mount -t smbfs -o username=user,password=pass //WinClient/share /mnt/share mount a windows network share   [man]
# nbtscan ip_addr netbios name resolution   [man]
# nmblookup -A ip_addr netbios name resolution   [man]
# smbclient -L ip_addr/hostname show remote shares of a windows host   [man]
# smbget -Rr smb://ip_addr/share like wget can download files from a host windows via smb   [man]
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IPTABLES (firewall)

Command Description
# iptables -t filter -L show all chains of filtering table   [man]
# iptables -t nat -L show all chains of nat table   [man]
# iptables -t filter -F clear all rules from filtering table   [man]
# iptables -t nat -F clear all rules from table nat   [man]
# iptables -t filter -X delete any chains created by user   [man]
# iptables -t filter -A INPUT -p tcp --dport telnet -j ACCEPT allow telnet connections to input   [man]
# iptables -t filter -A OUTPUT -p tcp --dport http -j DROP block HTTP connections to output   [man]
# iptables -t filter -A FORWARD -p tcp --dport pop3 -j ACCEPT allow POP3 connections to forward chain   [man]
# iptables -t filter -A INPUT -j LOG --log-prefix Logging on input chain   [man]
# iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE configure a PAT (Port Address Traslation) on eth0 masking outbound packets   [man]
# iptables -t nat -A PREROUTING -d 192.168.0.1 -p tcp -m tcp --dport 22 -j DNAT --to-destination 10.0.0.2:22 redirect packets addressed to a host to another host   [man]
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Monitoring and debugging

Command Description
# free -m displays status of RAM in megabytes   [man]
# kill -9 process_id force closure of the process and finish it   [man]
# kill -1 process_id force a process to reload configuration   [man]
# last reboot show history reboot   [man]
# lsmod display kernel loaded   [man]
# lsof -p process_id display a list of files opened by processes   [man]
# lsof /home/user1 displays a list of open files in a given path system   [man]
# ps -eafw displays linux tasks   [man]
# ps -e -o pid,args --forest displays linux tasks in a hierarchical mode   [man]
# pstree Shows a tree system processes   [man]
# smartctl -A /dev/hda monitoring reliability of a hard-disk through SMART   [man]
# smartctl -i /dev/hda check if SMART is active on a hard-disk   [man]
# strace -c ls >/dev/null display system calls made and received by a process   [man]
# strace -f -e open ls >/dev/null display library calls   [man]
# tail /var/log/dmesg show events inherent to the process of booting kernel   [man]
# tail /var/log/messages show system events   [man]
# top display linux tasks using most cpu   [man]
# watch -n1 'cat /proc/interrupts' display interrupts in real-time   [man]
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Other useful commands

Command Description
# alias hh='history' set an alias for a command - hh = history   [man]
# apropos ...keyword display a list of commands that pertain to keywords of a program , useful when you know what your program does, but you don't know the name of the command   [man]
# chsh change shell command   [man]
# chsh --list-shells nice command to know if you have to remote into another box   [man]
# gpg -c file1 encrypt a file with GNU Privacy Guard   [man]
# gpg file1.gpg decrypt a file with GNU Privacy Guard   [man]
# ldd /usr/bin/ssh show shared libraries required by ssh program   [man]
# man ping display the on-line manual pages for example on ping command - use '-k' option to find any related commands   [man]
# mkbootdisk --device /dev/fd0 `uname -r` create a boot floppy   [man]
# wget -r www.example.com download an entire web site   [man]
# wget -c www.example.com/file.iso download a file with the ability to stop the download and resume later   [man]
# echo 'wget -c www.example.com/files.iso' | at 09:00 start a download at any given time   [man]
# whatis ...keyword displays description of what a program does   [man]
# who -a show who is logged on, and print: time of last system boot, dead processes, system login processes, active processes spawned by init, current runlevel, last system clock change   [man]
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