Section (1) intro


Linux manual pages Section 1  

Name

intro — introduction to user commands

DESCRIPTION

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.

NOTES

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.

Login

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_zsingle_quotesz_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_zsingle_quotesz_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 ~.

Directories

The command mkdir makes a new directory.

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

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.

Processes

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.

SEE ALSO

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)

COLOPHON

This page is part of release 5.04 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 https://www.kernel.org/doc/man−pages/.


  Copyright (c) 2002 Andries Brouwer <aebcwi.nl>

%%%LICENSE_START(VERBATIM)
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

Since the Linux kernel and libraries are constantly changing, this
manual page may be incorrect or out-of-date.  The author(s) assume no
responsibility for errors or omissions, or for damages resulting from
the use of the information contained herein.  The author(s) may not
have taken the same level of care in the production of this manual,
which is licensed free of charge, as they might when working
professionally.

Formatted or processed versions of this manual, if unaccompanied by
the source, must acknowledge the copyright and authors of this work.
%%%LICENSE_END

Section (2) intro


Linux manual pages Section 2  

Name

intro — introduction to system calls

DESCRIPTION

Section 2 of the manual describes the Linux system calls. A system call is an entry point into the Linux kernel. Usually, system calls are not invoked directly: instead, most system calls have corresponding C library wrapper functions which perform the steps required (e.g., trapping to kernel mode) in order to invoke the system call. Thus, making a system call looks the same as invoking a normal library function.

In many cases, the C library wrapper function does nothing more than:

  • copying arguments and the unique system call number to the registers where the kernel expects them;

  • trapping to kernel mode, at which point the kernel does the real work of the system call;

  • setting errno if the system call returns an error number when the kernel returns the CPU to user mode.

However, in a few cases, a wrapper function may do rather more than this, for example, performing some preprocessing of the arguments before trapping to kernel mode, or postprocessing of values returned by the system call. Where this is the case, the manual pages in Section 2 generally try to note the details of both the (usually GNU) C library API interface and the raw system call. Most commonly, the main DESCRIPTION will focus on the C library interface, and differences for the system call are covered in the NOTES section.

For a list of the Linux system calls, see syscalls(2).

RETURN VALUE

On error, most system calls return a negative error number (i.e., the negated value of one of the constants described in errno(3)). The C library wrapper hides this detail from the caller: when a system call returns a negative value, the wrapper copies the absolute value into the errno variable, and returns −1 as the return value of the wrapper.

The value returned by a successful system call depends on the call. Many system calls return 0 on success, but some can return nonzero values from a successful call. The details are described in the individual manual pages.

In some cases, the programmer must define a feature test macro in order to obtain the declaration of a system call from the header file specified in the man page SYNOPSIS section. (Where required, these feature test macros must be defined before including any header files.) In such cases, the required macro is described in the man page. For further information on feature test macros, see feature_test_macros(7).

CONFORMING TO

Certain terms and abbreviations are used to indicate UNIX variants and standards to which calls in this section conform. See standards(7).

NOTES

Calling directly

In most cases, it is unnecessary to invoke a system call directly, but there are times when the Standard C library does not implement a nice wrapper function for you. In this case, the programmer must manually invoke the system call using syscall(2). Historically, this was also possible using one of the _syscall macros described in _syscall(2).

Authors and copyright conditions

Look at the header of the manual page source for the author(s) and copyright conditions. Note that these can be different from page to page!

SEE ALSO

_syscall(2), syscall(2), syscalls(2), errno(3), intro(3), capabilities(7), credentials(7), feature_test_macros(7), mq_overview(7), path_resolution(7), pipe(7), pty(7), sem_overview(7), shm_overview(7), signal(7), socket(7), standards(7), symlink(7), sysvipc(7), time(7)

COLOPHON

This page is part of release 5.04 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 https://www.kernel.org/doc/man−pages/.


  Copyright (C) 2007 Michael Kerrisk <mtk.manpagesgmail.com>

%%%LICENSE_START(VERBATIM)
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

Since the Linux kernel and libraries are constantly changing, this
manual page may be incorrect or out-of-date.  The author(s) assume no
responsibility for errors or omissions, or for damages resulting from
the use of the information contained herein.  The author(s) may not
have taken the same level of care in the production of this manual,
which is licensed free of charge, as they might when working
professionally.

Formatted or processed versions of this manual, if unaccompanied by
the source, must acknowledge the copyright and authors of this work.
%%%LICENSE_END

2007-10-23 mtk: moved the _syscallN specific material to the
    new _syscall(2) page, and substantially enhanced and rewrote
    the remaining material on this page.

Section (3) intro


Linux manual pages Section 3  

Name

intro — introduction to library functions

DESCRIPTION

Section 3 of the manual describes all library functions excluding the library functions (system call wrappers) described in Section 2, which implement system calls.

Many of the functions described in the section are part of the Standard C Library (libc Some functions are part of other libraries (e.g., the math library, libm or the real-time library, librt in which case the manual page will indicate the linker option needed to link against the required library (e.g., −lm and −lrt, respectively, for the aforementioned libraries).

In some cases, the programmer must define a feature test macro in order to obtain the declaration of a function from the header file specified in the man page SYNOPSIS section. (Where required, these feature test macros must be defined before including any header files.) In such cases, the required macro is described in the man page. For further information on feature test macros, see feature_test_macros(7).

CONFORMING TO

Certain terms and abbreviations are used to indicate UNIX variants and standards to which calls in this section conform. See standards(7).

NOTES

Authors and copyright conditions

Look at the header of the manual page source for the author(s) and copyright conditions. Note that these can be different from page to page!

SEE ALSO

intro(2), errno(3), capabilities(7), credentials(7), environ(7), feature_test_macros(7), libc(7), math_error(7), path_resolution(7), pthreads(7), signal(7), standards(7)

COLOPHON

This page is part of release 4.16 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 https://www.kernel.org/doc/man−pages/.


  Copyright (C) 2007 Michael Kerrisk <mtk.manpagesgmail.com>

%%%LICENSE_START(VERBATIM)
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

Since the Linux kernel and libraries are constantly changing, this
manual page may be incorrect or out-of-date.  The author(s) assume no
responsibility for errors or omissions, or for damages resulting from
the use of the information contained herein.  The author(s) may not
have taken the same level of care in the production of this manual,
which is licensed free of charge, as they might when working
professionally.

Formatted or processed versions of this manual, if unaccompanied by
the source, must acknowledge the copyright and authors of this work.
%%%LICENSE_END

2007-10-23 mtk, Nearly a complete rewrite of the earlier page.

Section (4) intro


Linux manual pages Section 4  

Name

intro — introduction to special files

DESCRIPTION

Section 4 of the manual describes special files (devices).

FILES

/dev/* — device files

NOTES

Authors and copyright conditions

Look at the header of the manual page source for the author(s) and copyright conditions. Note that these can be different from page to page!

SEE ALSO

mknod(1), mknod(2), standards(7)

COLOPHON

This page is part of release 4.16 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 https://www.kernel.org/doc/man−pages/.


  Copyright (c) 1993 Michael Haardt (michaelmoria.de),
    Fri Apr  2 11:32:09 MET DST 1993

%%%LICENSE_START(GPLv2+_DOC_FULL)
This is free documentation; you can redistribute it and/or
modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2 of
the License, or (at your option) any later version.

The GNU General Public License_zsingle_quotesz_s references to object code
and executables are to be interpreted as the output of any
document formatting or typesetting system, including
intermediate and printed output.

This manual is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public
License along with this manual; if not, see
<http://www.gnu.org/licenses/>.
%%%LICENSE_END

Modified Sat Jul 24 16:57:14 1993 by Rik Faith (faithcs.unc.edu)

Section (5) intro


Linux manual pages Section 5  

Name

intro — introduction to file formats and filesystems

DESCRIPTION

Section 5 of the manual describes various file formats, as well as the corresponding C structures, if any.

In addition, this section contains a number of pages that document various filesystems.

NOTES

Authors and copyright conditions

Look at the header of the manual page source for the author(s) and copyright conditions. Note that these can be different from page to page!

SEE ALSO

standards(7)

COLOPHON

This page is part of release 4.16 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 https://www.kernel.org/doc/man−pages/.


  Copyright (c) 1993 Michael Haardt (michaelmoria.de),
    Fri Apr  2 11:32:09 MET DST 1993

%%%LICENSE_START(GPLv2+_DOC_FULL)
This is free documentation; you can redistribute it and/or
modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2 of
the License, or (at your option) any later version.

The GNU General Public License_zsingle_quotesz_s references to object code
and executables are to be interpreted as the output of any
document formatting or typesetting system, including
intermediate and printed output.

This manual is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public
License along with this manual; if not, see
<http://www.gnu.org/licenses/>.
%%%LICENSE_END

Modified Sat Jul 24 17:06:52 1993 by Rik Faith (faithcs.unc.edu)
Modified Sun Jan 14 00:34:09 1996 by Andries Brouwer (aebcwi.nl)

Section (7) intro


Linux manual pages Section 7  

Name

intro — introduction to overview and miscellany section

DESCRIPTION

Section 7 of the manual provides overviews on various topics, and describes conventions and protocols, character set standards, the standard filesystem layout, and miscellaneous other things.

NOTES

Authors and copyright conditions

Look at the header of the manual page source for the author(s) and copyright conditions. Note that these can be different from page to page!

SEE ALSO

standards(7)

COLOPHON

This page is part of release 4.16 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 https://www.kernel.org/doc/man−pages/.


  Copyright (c) 1993 Michael Haardt
(michaelmoria.de), Fri Apr 2 11:32:09 MET DST
1993

%%%LICENSE_START(GPLv2+_DOC_FULL)
This is free documentation; you can redistribute it and/or
modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2 of
the License, or (at your option) any later version.

The GNU General Public License_zsingle_quotesz_s references to object code
and executables are to be interpreted as the output of any
document formatting or typesetting system, including
intermediate and printed output.

This manual is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public
License along with this manual; if not, see
<http://www.gnu.org/licenses/>.
%%%LICENSE_END

Modified by Thomas Koenig (ig25rz.uni-karlsruhe.de) 24 Apr 1993
Modified Sat Jul 24 17:28:08 1993 by Rik Faith (faithcs.unc.edu)

Section (8) intro


Linux manual pages Section 8  

Name

intro — introduction to administration and privileged commands

DESCRIPTION

Section 8 of the manual describes commands which either can be or are used only by the superuser, like system-administration commands, daemons, and hardware-related commands.

As with the commands described in Section 1, the commands described in this section terminate with an exit status that indicates whether the command succeeded or failed. See intro(1) for more information.

NOTES

Authors and copyright conditions

Look at the header of the manual page source for the author(s) and copyright conditions. Note that these can be different from page to page!

COLOPHON

This page is part of release 4.16 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 https://www.kernel.org/doc/man−pages/.


  Copyright (c) 1993 Michael Haardt (michaelmoria.de),
        Fri Apr  2 11:32:09 MET DST 1993
and Copyright (C) 2007 Michael Kerrisk <mtk.manpagesgmail.com>

%%%LICENSE_START(GPLv2+_DOC_FULL)
This is free documentation; you can redistribute it and/or
modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2 of
the License, or (at your option) any later version.

The GNU General Public License_zsingle_quotesz_s references to object code
and executables are to be interpreted as the output of any
document formatting or typesetting system, including
intermediate and printed output.

This manual is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public
License along with this manual; if not, see
<http://www.gnu.org/licenses/>.
%%%LICENSE_END

Modified Sat Jul 24 17:35:48 1993 by Rik Faith (faithcs.unc.edu)
2007-10-23 mtk: minor rewrites, and added paragraph on exit status