INTRO(1)                       Linux User's Manual                      INTRO(1)

       intro - introduction to user commands

       Section 1 of the manual describes user commands and tools, for example,
       file manipulation tools, shells, compilers, web browsers, file and image
       viewers and editors, and so on.

       Linux is a flavor of UNIX, and as a first approximation all user commands
       under UNIX work precisely the same under Linux (and FreeBSD and lots of
       other UNIX-like systems).

       Under Linux, there are GUIs (graphical user interfaces), where you can
       point and click and drag, and hopefully get work done without first
       reading lots of documentation.  The traditional UNIX environment is a CLI
       (command line interface), where you type commands to tell the computer
       what to do.  That is faster and more powerful, but requires finding out
       what the commands are.  Below a bare minimum, to get started.

       In order to start working, you probably first have to open a session by
       giving your username and password.  The program login(1) now starts a
       shell (command interpreter) for you.  In case of a graphical login, you
       get a screen with menus or icons and a mouse click will start a shell in
       a window.  See also xterm(1).

   The shell
       One types commands to the shell, the command interpreter.  It is not
       built-in, but is just a program and you can change your shell.  Everybody
       has their own favorite one.  The standard one is called sh.  See also
       ash(1), bash(1), chsh(1), csh(1), dash(1), ksh(1), zsh(1).

       A session might go like:

           knuth login: aeb
           Password: ********
           $ date
           Tue Aug  6 23:50:44 CEST 2002
           $ cal
                August 2002
           Su Mo Tu We Th Fr Sa
                        1  2  3
            4  5  6  7  8  9 10
           11 12 13 14 15 16 17
           18 19 20 21 22 23 24
           25 26 27 28 29 30 31

           $ ls
           bin  tel
           $ ls -l
           total 2
           drwxrwxr-x   2 aeb       1024 Aug  6 23:51 bin
           -rw-rw-r--   1 aeb         37 Aug  6 23:52 tel
           $ cat tel
           maja    0501-1136285
           peter   0136-7399214
           $ cp tel tel2
           $ ls -l
           total 3
           drwxr-xr-x   2 aeb       1024 Aug  6 23:51 bin
           -rw-r--r--   1 aeb         37 Aug  6 23:52 tel
           -rw-r--r--   1 aeb         37 Aug  6 23:53 tel2
           $ mv tel tel1
           $ ls -l
           total 3
           drwxr-xr-x   2 aeb       1024 Aug  6 23:51 bin
           -rw-r--r--   1 aeb         37 Aug  6 23:52 tel1
           -rw-r--r--   1 aeb         37 Aug  6 23:53 tel2
           $ diff tel1 tel2
           $ rm tel1
           $ grep maja tel2
           maja    0501-1136285

       Here typing Control-D ended the session.

       The $ here was the command prompt—it is the shell's way of indicating
       that it is ready for the next command.  The prompt can be customized in
       lots of ways, and one might include stuff like username, machine name,
       current directory, time, and so on.  An assignment PS1="What next,
       master? " would change the prompt as indicated.

       We see that there are commands date (that gives date and time), and cal
       (that gives a calendar).

       The command ls lists the contents of the current directory—it tells you
       what files you have.  With a -l option it gives a long listing, that
       includes the owner and size and date of the file, and the permissions
       people have for reading and/or changing the file.  For example, the file
       "tel" here is 37 bytes long, owned by aeb and the owner can read and
       write it, others can only read it.  Owner and permissions can be changed
       by the commands chown and chmod.

       The command cat will show the contents of a file.  (The name is from
       "concatenate and print": all files given as parameters are concatenated
       and sent to "standard output" (see stdout(3)), here the terminal screen.)

       The command cp (from "copy") will copy a file.

       The command mv (from "move"), on the other hand, only renames it.

       The command diff lists the differences between two files.  Here there was
       no output because there were no differences.

       The command rm (from "remove") deletes the file, and be careful! it is
       gone.  No wastepaper basket or anything.  Deleted means lost.

       The command grep (from "g/re/p") finds occurrences of a string in one or
       more files.  Here it finds Maja's telephone number.

   Pathnames and the current directory
       Files live in a large tree, the file hierarchy.  Each has a pathname
       describing the path from the root of the tree (which is called /) to the
       file.  For example, such a full pathname might be /home/aeb/tel.  Always
       using full pathnames would be inconvenient, and the name of a file in the
       current directory may be abbreviated by giving only the last component.
       That is why /home/aeb/tel can be abbreviated to tel when the current
       directory is /home/aeb.

       The command pwd prints the current directory.

       The command cd changes the current directory.

       Try alternatively cd and pwd commands and explore cd usage: "cd", "cd .",
       "cd ..", "cd /", and "cd ~".

       The command mkdir makes a new directory.

       The command rmdir removes a directory if it is empty, and complains

       The command find (with a rather baroque syntax) will find files with
       given name or other properties.  For example, "find . -name tel" would
       find the file tel starting in the present directory (which is called .).
       And "find / -name tel" would do the same, but starting at the root of the
       tree.  Large searches on a multi-GB disk will be time-consuming, and it
       may be better to use locate(1).

   Disks and filesystems
       The command mount will attach the filesystem found on some disk (or
       floppy, or CDROM or so) to the big filesystem hierarchy.  And umount
       detaches it again.  The command df will tell you how much of your disk is
       still free.

       On a UNIX system many user and system processes run simultaneously.  The
       one you are talking to runs in the foreground, the others in the
       background.  The command ps will show you which processes are active and
       what numbers these processes have.  The command kill allows you to get
       rid of them.  Without option this is a friendly request: please go away.
       And "kill -9" followed by the number of the process is an immediate kill.
       Foreground processes can often be killed by typing Control-C.

   Getting information
       There are thousands of commands, each with many options.  Traditionally
       commands are documented on man pages, (like this one), so that the
       command "man kill" will document the use of the command "kill" (and "man
       man" document the command "man").  The program man sends the text through
       some pager, usually less.  Hit the space bar to get the next page, hit q
       to quit.

       In documentation it is customary to refer to man pages by giving the name
       and section number, as in man(1).  Man pages are terse, and allow you to
       find quickly some forgotten detail.  For newcomers an introductory text
       with more examples and explanations is useful.

       A lot of GNU/FSF software is provided with info files.  Type "info info"
       for an introduction on the use of the program info.

       Special topics are often treated in HOWTOs.  Look in
       /usr/share/doc/howto/en and use a browser if you find HTML files there.

       ash(1), bash(1), chsh(1), csh(1), dash(1), ksh(1), locate(1), login(1),
       man(1), xterm(1), zsh(1), wait(2), stdout(3), man-pages(7), standards(7)

       This page is part of release 5.13 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                              2020-08-13                           INTRO(1)