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- This mapping will persist only in the logged session, if you want it make it permanent, you have to execute below command.
Let’s see some unique and important commands in Linux operating system rcp This command is used to copy files remotely from one machine to another. DESCRIPTION Rcp copies files between machines. Each file or directory argument is either a remote file name of the form ``rname@rhost:path'', or a local file name (containing no `:' characters, or a `/' before any `:'s). SCP scp is a program used to copy files between hosts on a network. It uses ssh(1) for data transfer, and uses the same authentication and provides the same security as ssh(1). Unlike rcp(1), scp will ask for passwords or passphrases if they are needed for authentication. Formate: scp [[username]@host1]:file1 [[username]@remote-host2]:[dir]
For eg. To copy a file from your system to any other system, use below command user1@host1:~> scp abc1.txt host2:~/test Enter Your Windows Password: abc1.txt 100% 19 0.0KB/s 00:00 The above command will copy the file abc1.txt of home directory of host1 to the ~/test directory of host2 If you dont specify any directory on the destination host, the file will be copied to home directory of remote host. Lets say: See below command: user1@host1:~> scp abc1.txt host2: Enter Your Windows Password: abc1.txt 100% 19 0.0KB/s 00:00 Printer related commands lp This command is used to send jobs for printing. If no printer specified, it will use the default destination. DESCRIPTION lp submits files for printing or alters a pending job. Use a filename of "-" to force printing from the standard input. The format is: SYNOPSIS lp [ -E ] [ -c ] [ -d destination ] [ -h server ] [ -m ] [ -n num-copies [ -o option ] [ -q priority ] [ -s ] [ -t title ] [ -H handling ] [ -P page-list ] [ file(s) ] Eg. Prompt:> lp abc.txt {ENTER} The file abc.txt will be sent for printing to the default printer You can use -d destination to specify the destination printer -h hostname Specifies the print server hostname. The default is "localhost" or the value of the CUPS_SERVER environment variable. lpr Same as lp, It also sends jobs for printing, if no destination specified, it used the default destinations. Format:
DESCRIPTION lpr submits files for printing. Files named on the command line are sent to the named printer (or the system default destination if no destination is specified). If no files are listed on the command-line lpr reads the print file from the standard input. lpadmin This command configure cups printers and classes Format: lpadmin [ -E ] [-U username ] [ -h server[:port] ] -d destination lpadmin [ -E ] [-U username ] [ -h server[:port] ] -p printer option(s) lpadmin [ -E ] [-U username ] [ -h server[:port] ] -x destination DESCRIPTION lpadmin configures printer and class queues provided by CUPS. It can also be used to set the server default printer or class. Example: lpadmin -U user1 -h cups-server:portno -p printer1 -v lpd://remoteserver/printer1 -o printer-is-shared=false -o printer-error-policy=retry-job -E lpadmin -U user1 -h cups-server:port -p printer2 -v lpd://remote-server/printer2 -o printer-is-shared=false -o printer-error-policy=retry-job -E lpstat This command shows the status of a CUPS printer. DESCRIPTION lpstat displays status information about the current classes, jobs, and printers. When run with no arguments, lpstat will list jobs queued by the current user. -a [printer(s)] Shows the accepting state of printer queues. If no printers are specified then all printers are listed. Eg. lpstat -a printer1 accepting requests since Tue 18 Feb 2014 11:15:04 AM CET printer2 accepting requests since Tue 18 Feb 2014 11:15:01 AM CET -c [class(es)] Shows the printer classes and the printers that belong to them. If no classes are specified then all classes are listed. -d
-h server[:port]
-l
-o [destination(s)]
-s
Eg. Prompt:>lpstat -s no system default destination device for printer1: lpd://server-name/printer1 device for printer2: lpd://server-name/printer2 lpinfo Thiscommand show available devices or drivers Format: lpinfo [ -E ] [ -U username ] [ -h server[:port] ] [ -l ] -m lpinfo [ -E ] [ -U username ] [ -h server[:port] ] [ -l ] -v DESCRIPTION lpinfo lists the available devices or drivers known to the CUPS server. The first form (-m) lists the available drivers, while the second form (-v) lists the available devices. lppasswd lppasswd - add, change, or delete digest passwords. Format:
lppasswd adds, changes, or deletes passwords in the CUPS digest password file, passwd.md5. When run by a normal user, lppasswd will prompt for the old and new passwords. When run by the super-user, lppasswd can add new accounts (-a user- name), change existing accounts (username), or delete accounts (-x username) in the digest password file. Digest usernames do not have to match local UNIX usernames. ps This command shows all the currently running processes DESCRIPTION:
It shows information in below format: UID PID PPID C STIME TTY TIME CMD UID -> User Id of the starter of the process PID -> Process id of the process PPID -> Process id of the parent process C -> STIME -> start time TTY TIME ->Duration by which the process is running CMD -> The command to start the process Example:
Prompt:>ps -fu userName This command will list all the process started by "userName" Prompt:>ps -aef This command will list all the process started by any user on the Linux machine. To see the every process on the system using BSD syntax, we can use folowwing command: ps -aux
man This command shows a help manual of any other command. It accepts a command-name as argument and shows a detailed help manual on that command. Example:
Prompt:>man man top Like ps, top command also shows currently running processes but it also updates their status repeatedly. Prompt:>top {} top - 12:59:25 up 82 days, 2:31, 6 users, load average: 0.31, 0.38, 0.36 Tasks: 257 total, 1 running, 255 sleeping, 0 stopped, 1 zombie Cpu(s): 0.0%us, 0.0%sy, 0.0%ni,100.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st Mem: 32782M total, 31096M used, 1685M free, 185M buffers Swap: 1027M total, 87M used, 940M free, 26222M cached It displays following details: PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND The command starts a display where all active processes are shown. It keeps on updating the values like % of CPU usage, % of memory usage, time the process is up by etc. whoami This command tells you who you are. It will tell the username who is logged on currently. For Eg. DESCRIPTION Print the user name associated with the current effective user ID. Same as id -un. Prompt:>whoami{Enter} user1 xev This command is ued to log the keyboard events. It starts an event tester and generates a log for evry keys pressed on the keyboard. DESCRIPTION
and development tool, and should not be needed in normal usage. For eg. Below is the log of Shift key and Enter key. Notice the 3rd line which gives the keycode , the key pressed and the screen where pressed. KeyPress event, serial 23, synthetic NO, window 0x400001, root 0x54, subw 0x0, time 759929, (601,628), root:(605,654), state 0x0, keycode 61 (keysym 0xffe2, Shift_R), same_screen YES, XLookupString gives 0 bytes: XmbLookupString gives 0 bytes: XFilterEvent returns: False KeyRelease event, serial 25, synthetic NO, window 0x400001, root 0x54, subw 0x0, time 760088, (601,628), root:(605,654), state 0x1, keycode 61 (keysym 0xffe2, Shift_R), same_screen YES, XLookupString gives 0 bytes: XFilterEvent returns: False KeyPress event, serial 25, synthetic NO, window 0x400001, root 0x54, subw 0x0, time 761329, (601,628), root:(605,654), state 0x0, keycode 35 (keysym 0xff0d, Return), same_screen YES, " XLookupString gives 1 bytes: (0d) " " XmbLookupString gives 1 bytes: (0d) " XFilterEvent returns: False KeyRelease event, serial 25, synthetic NO, window 0x400001, root 0x54, subw 0x0, time 761469, (601,628), root:(605,654), state 0x0, keycode 35 (keysym 0xff0d, Return), same_screen YES, " XLookupString gives 1 bytes: (0d) " XFilterEvent returns: FalseThis command is ued to log the keyboard events. It starts an event tester and generates a log for evry keys pressed on the keyboard. DESCRIPTION Xev creates a window and then asks the X server to send it events whenever anything happens to the window (such as it being moved, resized, typed in, clicked in, etc.). You can also attach it to an existing window. It is useful for seeing what causes events to occur and to display the information that they contain; it is essentially a debugging and development tool, and should not be needed in normal usage. For eg. Below is the log of Shift key and Enter key. Notice the 3rd line which gives the keycode , the key pressed and the screen where pressed. KeyPress event, serial 23, synthetic NO, window 0x400001, root 0x54, subw 0x0, time 759929, (601,628), root:(605,654), state 0x0, keycode 61 (keysym 0xffe2, Shift_R), same_screen YES, XLookupString gives 0 bytes: XmbLookupString gives 0 bytes: XFilterEvent returns: False KeyRelease event, serial 25, synthetic NO, window 0x400001, root 0x54, subw 0x0, time 760088, (601,628), root:(605,654), state 0x1, keycode 61 (keysym 0xffe2, Shift_R), same_screen YES, XLookupString gives 0 bytes: XFilterEvent returns: False KeyPress event, serial 25, synthetic NO, window 0x400001, root 0x54, subw 0x0, time 761329, (601,628), root:(605,654), state 0x0, keycode 35 (keysym 0xff0d, Return), same_screen YES, " XLookupString gives 1 bytes: (0d) " " XmbLookupString gives 1 bytes: (0d) " XFilterEvent returns: False KeyRelease event, serial 25, synthetic NO, window 0x400001, root 0x54, subw 0x0, time 761469, (601,628), root:(605,654), state 0x0, keycode 35 (keysym 0xff0d, Return), same_screen YES, " XLookupString gives 1 bytes: (0d) " XFilterEvent returns: False xmodmap This command is used to remap the keyboard keys from one to another or as per user's choice. Suppose your Enter key is not working, you can use your right shift key by mapping Enter key to the it. DESCRIPTION
So to map the right shift key to your enter key, use below command: xmodmap -e "keycode 61=Return" xmodmap -e "keycode 35=Shift_R" The format is: xmodmap -e EXPRESSION. The expression can be: keycode NUMBER=KEYSYMNAME This mapping will persist only in the logged session, if you want it make it permanent, you have to execute below command. xmodmap -pke >~/.Xmodmap It will create a file Xmodmap in your home directory. Then create one more file called .xinitrc in your home directory where you have to enter this line: xmodmap .Xmodmap ping This command is used to ping an ip-address or server to find if the host is in the n/w or reachable. It takes ip address or ip-name as argument. DESCRIPTION: ping uses the ICMP protocol's mandatory ECHO_REQUEST datagram to elicit an ICMP ECHO_RESPONSE from a host or gateway. On success: Linux-Prompt:> ping serverOrIP PING serverOrIP (1.2.3.4) 56(84) bytes of data. 64 bytes from serverOrIP (1.2.3.4): icmp_seq=1 ttl=58 time=0.365 ms 64 bytes from serverOrIP (1.2.3.4): icmp_seq=2 ttl=58 time=0.435 ms 64 bytes from serverOrIP (1.2.3.4): icmp_seq=3 ttl=58 time=0.345 ms --- serverOrIP ping statistics --- 3 packets transmitted, 3 received, 0% packet loss, time 2005ms rtt min/avg/max/mdev = 0.345/0.381/0.435/0.044 ms On failure: It says: Unknown host or ping failure.
The command shows all the active internet connection. DESCRIPTION: Netstat prints information about the Linux networking subsystem. The type of information printed is controlled by the first argument, as follows: (none) By default, netstat displays a list of open sockets. If you don't specify any address families, then the active sockets of all configured address families will be printed. It shows following information: Proto Recv-Q Send-Q Local Address Foreign Address State nmap The command accepts ip-address or Ip-name as argument. It is used to show the status of all open ports on that IP-address. DESCRIPTION
PORT STATE SERVICE 25/tcp open smtp 80/tcp open http 139/tcp open netbios-ssn 443/tcp open https 515/tcp open printer 631/tcp open ipp 843/tcp open unknown 9100/tcp open jetdirect 50003/tcp open unknown Nmap done: 1 IP address (1 host up) scanned in 6.61 seconds
history This command displays a list of recently executed commands on your session with the timestamp. Eg. Prompt:>history 1 2014-02-20 15:25:18 netstat 2 2014-02-20 15:29:51 man history 3 2014-02-20 15:30:28 history
The commands is used to change access permission to a file. I can add access permission, remove access permissions. Refer below example: Prompt:>ls -l abc.txt -rw-rw-r-- 1 someUser someGroup 27 2014-02-20 15:37 abc.txt Prompt:>chmod 777 abc.txt Prompt:>ll abc.txt -rwxrwxrwx 1 someUser someGroup 27 2014-02-20 15:37 abc.txt User someUser had permission -rw-rw-r--(664) on the file abc.txt by default.
This command changes the group and owneship of a file Description: chown changes the user and/or group ownership of each given file. If only an owner (a user name or numeric user ID) is given, that user is made the owner of each given file, and the files' group is not changed. If the owner is followed by a colon and a group name (or numeric group ID), with no spaces between them, the group ownership of the files is changed as well. Examples:
This command starts a funny animation. It will start a small window containing animation of eyes. And, the eyes will look where your cursor goes. To quit press ctrl+c . emacs
This command is used to read a documentation in info format. Example Prompt:>info emacs {ENTER} Prompt:>info show top-level dir menu At the info page, press p -> to go to previous node(data) n -> to the nest node or entry spacebar -> to go below. The last two lines of the content will be at the top of the page and more lines will be displayed. Del/backspace -> to come back (undo of spacebar) portmap
file A command to determine the type of file. It takes a file as argument and tells its type DESCRIPTION file tests each argument in an attempt to classify it. There are three sets of tests, performed in this order: filesystem tests, magic tests, and language tests. The first test that succeeds causes the file type to be printed. Eg. Prompt:>file abc.txt abc.txt: ASCII text Prompt:> file abc.xml abc.xml: XML Prompt:>ll LinkFile lrwxrwxrwx 1 username group 44 2013-08-01 09:39 LinkFile -> ~/a/b/c/somescript.sh Prompt:>file LinkFile LinkFile: symbolic link to `~/a/b/c/somescript.sh' type This command accepts the command-name as argument and tells the type of command. It writes about the command like it is a shell builtin command or an alias or a bin command. Eg. Prompt:> type alias alias is a shell builtin Prompt:> type whoami whoami is /usr/bin/whoami Prompt:> type ll ll is aliased to `ls -la'
A shell builtin command that shows aliases being used currently in your system. You can set aliases as per need to shorten the long commands and customize the commands. For Eg. alias ll='ls -l' It will set "ls -l" command to "ll" and "ll " will work as "ls -l" To set an alias, use below format: alias customCommand='complex set of comands'
It takes server-name or ip-address as argument. This command is used to query the DNS and find the alias names of a server. It gives all the canonical and logical names and ip-address for a server or ip-adress. Description:Nslookup is a program to query Internet domain name servers. Nslookup
Eg. nslookup ip-address/server host Takes server/ip-name as argument.This command will tell you the alias name and ip- address of the server-name DESCRIPTION: host is a simple utility for performing DNS lookups. It is normally used to convert names to IP addresses and vice versa. uname It displays system information. "uname -a" will give a long system description. Eg. Prompt:>uname -a Linux hostname 2.6.32.59-0.3-xen #1 SMP 2012-04-27 11:14:44 +0200 x86_64 x86_64 x86_64 GNU/Linux finger DESCRIPTION The finger utility displays information about local and remote system users. By default, the following information is displayed about each user currently logged-in to the local host: · login name · user's full name · associated terminal name · idle time · login time · from where id This command is used to find the user id and group id of a user. It also shows the groups the user belongs to. Eg. Prompt :> id uid=12345(someid) gid=12345(groupname) groups=gid(gname), gid(gname)...
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