1. Command: ls
The command “ls” stands for (List Directory Contents), List the contents of the folder, be it file or folder, from which it runs.
root@tecmint:~# ls Android-Games Music Pictures Public Desktop Tecmint.com Documents TecMint-Sync Downloads Templates
The command “ls -l” list the content of folder, in long listing fashion.
root@tecmint:~# ls -l total 40588 drwxrwxr-x 2 ravisaive ravisaive 4096 May 8 01:06 Android Games drwxr-xr-x 2 ravisaive ravisaive 4096 May 15 10:50 Desktop drwxr-xr-x 2 ravisaive ravisaive 4096 May 16 16:45 Documents drwxr-xr-x 6 ravisaive ravisaive 4096 May 16 14:34 Downloads drwxr-xr-x 2 ravisaive ravisaive 4096 Apr 30 20:50 Music drwxr-xr-x 2 ravisaive ravisaive 4096 May 9 17:54 Pictures drwxrwxr-x 5 ravisaive ravisaive 4096 May 3 18:44 Tecmint.com drwxr-xr-x 2 ravisaive ravisaive 4096 Apr 30 20:50 Templates
Command “ls -a“, list the content of folder, including hidden files starting with ‘.’.
root@tecmint:~# ls -a . .gnupg .dbus .goutputstream-PI5VVW .mission-control .adobe deja-dup .grsync .mozilla .themes .gstreamer-0.10 .mtpaint .thumbnails .gtk-bookmarks .thunderbird .HotShots .mysql_history .htaccess .apport-ignore.xml .ICEauthority .profile .bash_history .icons .bash_logout .fbmessenger .jedit .pulse .bashrc .liferea_1.8 .pulse-cookie .Xauthority .gconf .local .Xauthority.HGHVWW .cache .gftp .macromedia .remmina .cinnamon .gimp-2.8 .ssh .xsession-errors .compiz .gnome teamviewer_linux.deb .xsession-errors.old .config .gnome2 .zoncolor
Note: In Linux file name starting with ‘.‘ is hidden. In Linux every file/folder/device/command is a file. The output of ls -l is:
- d (stands for directory).
- rwxr-xr-x is the file permission of the file/folder for owner, group and world.
- The 1st ravisaive in the above example means that file is owned by user ravisaive.
- The 2nd ravisaive in the above example means file belongs to user group ravisaive.
- 4096 means file size is 4096 Bytes.
- May 8 01:06 is the date and time of last modification.
- And at the end is the name of the File/Folder.
2. Command: lsblk
The “lsblk” stands for (List Block Devices), print block devices by their assigned name (but not RAM) on the standard output in a tree-like fashion.
root@tecmint:~# lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT sda 8:0 0 232.9G 0 disk ├─sda1 8:1 0 46.6G 0 part / ├─sda2 8:2 0 1K 0 part ├─sda5 8:5 0 190M 0 part /boot ├─sda6 8:6 0 3.7G 0 part [SWAP] ├─sda7 8:7 0 93.1G 0 part /data └─sda8 8:8 0 89.2G 0 part /personal sr0 11:0 1 1024M 0 rom
The “lsblk -l” command list block devices in ‘list‘ structure (not tree like fashion).
root@tecmint:~# lsblk -l NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT sda 8:0 0 232.9G 0 disk sda1 8:1 0 46.6G 0 part / sda2 8:2 0 1K 0 part sda5 8:5 0 190M 0 part /boot sda6 8:6 0 3.7G 0 part [SWAP] sda7 8:7 0 93.1G 0 part /data sda8 8:8 0 89.2G 0 part /personal sr0 11:0 1 1024M 0 rom
Note: lsblk is very useful and easiest way to know the name of New Usb Device you just plugged in, especially when you have to deal with disk/blocks in terminal.
3. Command: md5sum
The “md5sum” stands for (Compute and Check MD5 Message Digest), md5 checksum (commonly called hash) is used to match or verify integrity of files that may have changed as a result of a faulty file transfer, a disk error or non-malicious interference.
root@tecmint:~# md5sum teamviewer_linux.deb 47790ed345a7b7970fc1f2ac50c97002 teamviewer_linux.deb
Note: The user can match the generated md5sum with the one provided officially. Md5sum is considered less secure than sha1sum, which we will discuss later.
4. Command: dd
Command “dd” stands for (Convert and Copy a file), Can be used to convert and copy a file and most of the times is used to copy a iso file (or any other file) to a usb device (or any other location), thus can be used to make a ‘Bootlable‘ Usb Stick.
root@tecmint:~# dd if=/home/user/Downloads/debian.iso of=/dev/sdb1 bs=512M; sync
Note: In the above example the usb device is supposed to be sdb1 (You should Verify it using command lsblk, otherwise you will overwrite your disk and OS), use name of disk very Cautiously!!!.
dd command takes some time ranging from a few seconds to several minutes in execution, depending on the size and type of file and read and write speed of Usb stick.
5. Command: uname
The “uname” command stands for (Unix Name), print detailed information about the machine name, Operating System and Kernel.
root@tecmint:~# uname -a Linux tecmint 3.8.0-19-generic #30-Ubuntu SMP Wed May 1 16:36:13 UTC 2013 i686 i686 i686 GNU/Linux
Note: uname shows type of kernel. uname -a output detailed information. Elaborating the above output of uname -a.
- “Linux“: The machine’s kernelhostname
- “tecmint“: The machine’s node name.
- “3.8.0-19-generic“: The kernel release.
- “#30-Ubuntu SMP“: The kernel version.
- “i686“: The architecture of the processor.
- “GNU/Linux“: The operating system name.
6. Command: history
The “history” command stands for History (Event) Record, it prints the history of long list of executed commands in terminal.
root@tecmint:~# history 1 sudo add-apt-repository ppa:tualatrix/ppa 2 sudo apt-get update 3 sudo apt-get install ubuntu-tweak 4 sudo add-apt-repository ppa:diesch/testing 5 sudo apt-get update 6 sudo apt-get install indicator-privacy 7 sudo add-apt-repository ppa:atareao/atareao 8 sudo apt-get update 9 sudo apt-get install my-weather-indicator 10 pwd 11 cd && sudo cp -r unity/6 /usr/share/unity/ 12 cd /usr/share/unity/icons/ 13 cd /usr/share/unity
Note: Pressing “Ctrl + R” and then search for already executed commands which lets your command to be completed with auto completion feature.
(reverse-i-search)`if': ifconfig
7. Command: sudo
The “sudo” (super user do) command allows a permitted user to execute a command as the superuser or another user, as specified by the security policy in the sudoers list.
root@tecmint:~# sudo add-apt-repository ppa:tualatrix/ppa
Note: sudo allows user to borrow superuser privileged, while a similar command ‘su‘ allows user to actually log in as superuser. Sudo is safer than su.
It is not advised to use sudo or su for day-to-day normal use, as it can result in serious error if accidentally you did something wrong, that’s why a very popular saying in Linux community is:
“To err is human, but to really foul up everything, you need root password.”
8. Command: mkdir
The “mkdir” (Make directory) command create a new directory with name path. However is the directory already exists, it will return an error message “cannot create folder, folder already exists”.
root@tecmint:~# mkdir tecmint
Note: Directory can only be created inside the folder, in which the user has write permission. mkdir:tecmint creattecminttory `tecmint‘: File exists
(Don’t confuse with file in the above output, you might remember what i said at the beginning – In Linux every file, folder, drive, command, scripts are treated as file).
9. Command: touch
The “touch” command stands for (Update the access and modification times of each FILE to the current time). touch command creates the file, only if it doesn’t exist. If the file already exists it will update the timestamp and not the contents of the file.
root@tecmint:~# touch tecmintfile
Note: touch can be used to create file under directory, on which the user has write permission, only if the file don’t exist there.
10. Command: chmod
The Linux “chmod” command stands for (change file mode bits). chmod changes the file mode (permission) of each given file, folder, script, etc.. according to mode asked for.
There exist 3 types of permission on a file (folder or anything but to keep things simple we will be using file).
Read (r)=4 Write(w)=2 Execute(x)=1
So if you want to give only read permission on a file it will be assigned a value of ‘4‘, for write permission only, a value of ‘2‘ and for execute permission only, a value of ‘1‘ is to be given. For read and write permission 4+2 = ‘6‘ is to be given, ans so on.
Now permission need to be set for 3 kinds of user and usergroup. The first is owner, then usergroup and finally world.
rwxr-x--x abc.sh
Here the root’s permission is rwx (read, write and execute).
usergroup to which it belongs, is r-x (read and execute only, no write permission) and
for world is –x (only execute).
To change its permission and provide read, write and execute permission to owner, group and world.
root@tecmint:~# chmod 777 abc.sh
only read and write permission to all three.
root@tecmint:~# chmod 666 abc.sh
read, write and execute to owner and only execute to group and world.
root@tecmint:~# chmod 711 abc.sh
Note: one of the most important command useful for sysadmin and user both. On a multi-user environment or on a server, this command comes to rescue, setting wrong permission will either makes a file inaccessible or provide unauthorized access to someone.
11. Command: chown
The Linux “chown” command stands for (change file owner and group). Every file belongs to a group of user and a owner. It is used Do ‘ls -l‘ into your directory and you will see something like this.
root@tecmint:~# ls -l drwxr-xr-x 3 server root 4096 May 10 11:14 Binary drwxr-xr-x 2 server server 4096 May 13 09:42 Desktop
Here the directory Binary is owned by user “server” and it belongs to usergroup “root” where as directory “Desktop” is owned by user “server” and belongs to user group “server“.
This “chown” command is used to change the file ownership and thus is useful in managing and providing file to authorised user and usergroup only.
root@tecmint:~# chown server:server Binary drwxr-xr-x 3 server server 4096 May 10 11:14 Binary drwxr-xr-x 2 server server 4096 May 13 09:42 Desktop
Note: “chown” changes the user and group ownership of each given FILE to NEW-OWNER or to the user and group of an existing reference file.
12. Command: apt
The Debian based “apt” command stands for (Advanced Package Tool). Apt is an advanced package manager for Debian based system (Ubuntu, Kubuntu, etc.), that automatically and intelligently search, install, update and resolves dependency of packages on Gnu/Linuxsystem from command line.
root@tecmint:~# apt-get install mplayer Reading package lists... Done Building dependency tree Reading state information... Done The following package was automatically installed and is no longer required: java-wrappers Use 'apt-get autoremove' to remove it. The following extra packages will be installed: esound-common libaudiofile1 libesd0 libopenal-data libopenal1 libsvga1 libvdpau1 libxvidcore4 Suggested packages: pulseaudio-esound-compat libroar-compat2 nvidia-vdpau-driver vdpau-driver mplayer-doc netselect fping The following NEW packages will be installed: esound-common libaudiofile1 libesd0 libopenal-data libopenal1 libsvga1 libvdpau1 libxvidcore4 mplayer 0 upgraded, 9 newly installed, 0 to remove and 8 not upgraded. Need to get 3,567 kB of archives. After this operation, 7,772 kB of additional disk space will be used. Do you want to continue [Y/n]? y
root@tecmint:~# apt-get update Hit http://ppa.launchpad.net raring Release.gpg Hit http://ppa.launchpad.net raring Release.gpg Hit http://ppa.launchpad.net raring Release.gpg Hit http://ppa.launchpad.net raring Release.gpg Get:1 h
