Technical Club



Linux Shortcuts and Commands:(Part I)

This is a practical selection of the commands we use most often. Press <Tab> to see the listing of all available command (on your PATH). On my small home system, it says there are 2595 executables on my PATH.  Many of these “commands” can be accessed from your favourite GUI front-end (probably KDE or Gnome) by clicking on the right menu or button. They can all be run from the command line.  Programs that require GUI have to be run from a terminal opened under a GUI.

Legend:
<> = single special or function key on the keyboard. For example <Ctrl> indicates the “control” key.
italic = name of the file or variable you probably want to substitute with your own.
fixed width = in-line Linux commands and filenames.

Notes for the UNIX Clueless:
1. LINUX IS CASE-SENSITIVE. For example: Netscape, NETSCAPE and nEtscape are three different commands. Also my_filE, my_file, and my_FILE are three different files. Your user login name and password are also case sensitive. (This goes with the tradition of UNIX and the “c” programming language being case sensitive.)
2. Filenames can be up to 256 characters long and can contain letters, numbers, “.” (dot), “_” (underscore), “-” (dash), plus some other not recommended characters.
3. Files with names starting with “.” are normally not shown by the ls (list) or dir commands. Think of these files as “hidden”. Use ls -a  (list with the option “all”) to see these files.
4. “/” is an equivalent to DOS “\” (root directory, meaning the parent of all other directories).
5. Under Linux, all directories appear under a single directory tree (there are no DOS-style drive letters).
6. In a configuration file, a line starting with # is a comment.

7.1 Linux essential shortcuts and sanity commands

<Ctrl><Alt><F1>
Switch to the first text terminal. Under Linux you can have several (6 in standard setup) terminals opened at the same time.

<Ctrl><Alt><Fn> (n=1..6)
Switch to the nth text terminal.

tty
Print the name of the terminal in which you are typing this command.

<Ctrl><Alt><F7>
Switch to the first GUI terminal (if X-windows is running on this terminal).

<Ctrl><Alt><Fn> (n=7..12)
Switch to the nth GUI terminal (if a GUI terminal is running on screen n-1). On default, nothing is running on terminals
8 to 12, but you can run another server there.

<Tab>
(In a text terminal) Autocomplete the command  if there is only one option, or else show all the available options.
THIS SHORTCUT IS GREAT! It even works at LILO prompt!

<ArrowUp>
Scroll and edit the command history. Press <Enter> to execute.

<Shift><PgUp>
Scroll terminal output up. Work also at the login prompt, so you can scroll through your bootup messages.

<Shift><PgDown>
Scroll terminal output down.

<Ctrl><Alt><+>
(in X-windows) Change to the next X-server resolution (if you set up the X-server to more than one resolution). For multiple resolutions on my standard SVGA card/monitor, I have the following line in the file /etc/X11/XF86Config (the first resolution starts on default, the largest determines the size of the “virtual screen”):
Modes “1024×768” “800×600” “640×480” “512×384” “480×300” “400×300” “1152×864”

<Ctrl><Alt><->
(in X-windows) Change to the previous X-server resolution.

<Ctrl><Alt><BkSpc>
(in X-windows) Kill the current X-windows server. Use if the X-windows server crushes and cannot be exited normally.

<Ctrl><Alt><Del>
Shut down the system and reboot. This is the normal shutdown command for a user at the text-mode console. Don’t just press the “reset” button for shutdown!

<Ctrl>c
Kill the current process (mostly in the text mode for small applications).

<Ctrl>d
Log out from the current terminal.  See also the next command.

<Ctrl>d
Send [End-of-File] to the current process. Don’t press it twice else you also log out (see the previous command).

<Ctrl>s
Stop the transfer to the terminal.

<Ctrl>q
Resume the transfer to the terminal. Try if your terminal mysteriously stops responding.

<Ctrl>z
Send the current process to the background.

exit
Logout. I can also use logout for the same effect.  (If you have started a second shell, e.g., using bash the second shell will be exited and you will be back in the first shell, not logged out.)

reset
Restore a screwed-up terminal (a terminal showing funny characters) to default setting. Use if you tried to “cat” a binary file. You may not be able to see the command as you type it.

<MiddleMouseButton>
Paste the text which is currently highlighted somewhere else. This is the normal “copy-paste” operation in Linux.  (It doesn’t work with Netscape and WordPerfect which use the MS Windows-style “copy-paste”. It does work in the text terminal if you enabled “gpm” service using “setup”.) Best used with a Linux-ready 3-button mouse (Logitech or similar) or else set “3-mouse button emulation”).

~
(tilde) My home directory (normally the directory /home/my_login_name). For example, the command cd ~/my_dir will change my working  directory to the subdirectory “my_dir” under my home directory.  Typing just “cd” alone is an equivalent of the command “cd ~”.

.
(dot) Current directory. For example, ./my_program will attempt to execute the file “my_program” located in your current working directory.

..
(two dots) Directory parent to the current one. For example, the command cd .. will change my current working directory one one level up.

7.2 Common Linux commands–system info

pwd
Print working directory, i.e., display the name of my current directory on the screen.

hostname
Print the name of the local host (the machine on which you are working). Use netconf (as root) to change the name of the machine.

whoami
Print my login name.

id username
Print user id (uid) and his/her group id (gid), effective id (if different than the real id) and the supplementary groups.

date
Print or change the operating system date and time. E.g., I could change the date and time to 2000-12-31 23:57 using this command:
date 123123572000
To set the hardware (BIOS) clock from the system (Linux) clock, use the command (as root) setclock

time
Determine the amount of time that it takes for a process to complete + other info. Don’t confuse it with the date command. E.g. I can find out how long it takes to display a directory content using:
time ls

who
Determine the users logged on the machine.

rwho -a
(=remote who) Determine all users logged on your network. The rwho service must be enabled for this command to run. If it isn’t, run setup as root to enable “rwho”.

finger user_name
System info about a user. Try: finger root

last
Show listing of users last logged-in on your system.

history | more
Show the last (1000 or so) commands executed from the command line on the current account. The “| more” causes the display to stop after each screenful.

uptime
Show the amount of time since the last reboot.

ps
(=print status) List the processes currently run by the current user.

ps axu | more
List all the processes currently running, even those without the controlling terminal, together with the name of the user that owns each process.

top
Keep listing the currently running processes, sorted by cpu usage (top users first). In KDE, you can get GUI-based Ktop from “K”menu under “System”-“Task Manager” (or by executing “ktop” in an X-terminal).

uname -a
(= Unix name with option “all”) Info on your (local) server. I can also use guname (in X-window terminal) to display the info more nicely.

free
Memory info (in kilobytes).

df -h
(=disk free) Print disk info about all the filesystems (in human-readable form)

du / -bh | more
(=disk usage) Print detailed disk usage for each subdirectory starting at the “/” (root) directory (in human legible form).

cat /proc/cpuinfo
Cpu info–it show the content of the file cpuinfo. Note that the files in the /proc directory are not real files–they are hooks to look at information available to the kernel.

cat /proc/interrupts
List the interrupts in use.

cat /proc/version
Linux version and other info

cat /proc/filesystems
Show the types of filesystems currently in use.

cat /etc/printcap
Show the setup of printers.

lsmod
(As root. Use /sbin/lsmod to execute this command when you are a non-root user.) Show the kernel modules currently loaded.

set|more
Show the current user environment.

echo $PATH
Show the content of the environment variable “PATH”. This command can be used to show other environment variables as well. Use “set” to see the full environment.

dmesg | less
Print kernel messages (the content of the so-called kernel ring buffer). Press “q” to quit “less”. Use less /var/log/dmesg  to see what “dmesg” dumped into this file right after the last system bootup.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: