Linux man pages
---------------
Sections
Manual pages are grouped into sections based upon the type of command,
function, or file they describe.
Section 1
user commands
Section 2
system calls
This chapter describes the Linux system calls. For a list of the
164 syscalls present in Linux 2.0, see syscalls(2)
Section 3
library functions
This chapter describes all library functions excluding the
library functions described in chapter 2, which implement system
calls
Section 4
special files
This chapter describes special files.
/dev/* --- device files
Section 5
file formats
This chapter describes various file formats and protocols, and
the used C structures, if any
Section 6
games
This chapter describes all the games and funny little programs
available on the system
Section 7
conventions and miscellany
This chapter describes conventions and protocols, character set
standards, the standard file system layout, and miscellaneous
other things
Section 8
administration and privileged commands
This chapter describes commands which either can be or are only
used by the superuser, like daemons and hardware related commands
Section L
math library functions
This chapter describes commands which either can be or are only
used by the superuser, like daemons and hardware related commands.
Section N
tcl fuctions
intro - Introduction to user commands
-------------------------------------
Linux is a flavour 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 login, that is,
give your username and password. See also login(1). The program login
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 her own favourite one. The standard one is called sh.
See also ash(1), bash(1), csh(1), zsh(1), chsh(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
%
and 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 user name, machine name, current directory,
time, etc. 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", here the terminal screen.)
The command cp (from "copy") will copy a file. On the other hand, the
command mv (from "move") 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.
Path names and the current directory
Files live in a large tree, the file hierarchy. Each has a path name
describing the path from the root of the tree (which is called /) to
the file. For example, such a full path name might be /home/aeb/tel.
Always using full path names would be inconvenient, and the name of a
file in the current directory may be abbreviated by only giving 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 "cd /" and "pwd" and
"cd" and "pwd".
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 custumary 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.
intro, _syscall - Introduction to system calls
----------------------------------------------
This chapter describes the Linux system calls. For a list of the 164
syscalls present in Linux 2.0, see syscalls(2).
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
function call for you.
Synopsis
#include
A _syscall macro
desired system call
Setup
The important thing to know about a system call is its prototype. You
need to know how many arguments, their types, and the function return
type. There are six macros that make the actual call into the system
easier. They have the form:
_syscallX(type,name,type1,arg1, type2,arg2,...)
where X is 0-5, which are the number of arguments taken by the system
call type is the return type of the system call
name is the name of the system call
typeN is the Nth argument's type
argN is the name of the Nth argument
These macros create a function called name with the arguments you
specify. Once you include the _syscall() in your source file, you call
the system call by name.
example
#include
#include
#include /* for _syscallX macros/related stuff */
#include /* for struct sysinfo */
_syscall1(int, sysinfo, struct sysinfo *, info);
/* Note: if you copy directly from the nroff source, remember to
REMOVE the extra backslashes in the printf statement. */
int main(void)
{
struct sysinfo s_info;
int error;
error = sysinfo(&s_info);
printf("code error = %d\n", error);
printf("Uptime = %lds\nLoad: 1 min %lu / 5 min %lu / 15 min %lu\n"
"RAM: total %lu / free %lu / shared %lu\n"
"Memory in buffers = %lu\nSwap: total %lu / free %lu\n"
"Number of processes = %d\n",
s_info.uptime, s_info.loads[0],
s_info.loads[1], s_info.loads[2],
s_info.totalram, s_info.freeram,
s_info.sharedram, s_info.bufferram,
s_info.totalswap, s_info.freeswap,
s_info.procs);
return(0);
}
Sample Output
code error = 0
uptime = 502034s
Load: 1 min 13376 / 5 min 5504 / 15 min 1152
RAM: total 15343616 / free 827392 / shared 8237056
Memory in buffers = 5066752
Swap: total 27881472 / free 24698880
Number of processes = 40
notes
The _syscall() macros DO NOT produce a prototype. You may have to
create one, especially for C++ users.
System calls are not required to return only positive or negative
error codes. You need to read the source to be sure how it will return
errors. Usually, it is the negative of a standard error code, e.g.,
-EPERM. The _syscall() macros will return the result r of the system
call when r is nonnegative, but will return -1 and set the variable
errno to -r when r is negative. For the error codes, see errno(3).
Some system calls, such as mmap, require more than five arguments.
These are handled by pushing the arguments on the stack and passing a
pointer to the block of arguments.
When defining a system call, the argument types MUST be passed by-value
or by-pointer (for aggregates like structs).
The preferred way to invoke system calls that glibc does not know about
yet, is via syscall(2).
Conforming to
Certain codes are used to indicate Unix variants and standards to which
calls in the section conform. These are:
SVr4 System V Release 4 Unix, as described in the "Programmer's
Reference Manual: Operating System API (Intel processors)"
(Prentice-Hall 1992, ISBN 0-13-951294-2)
SVID System V Interface Definition, as described in
"The System V Interface Definition, Fourth Edition".
POSIX.1 IEEE 1003.1-1990 part 1, aka ISO/IEC 9945-1:1990s,
aka "IEEE Portable Operating System Interface for
Computing Environments", as elucidated in Donald Lewine's
"POSIX Programmer's Guide" (O'Reilly & Associates, Inc.,
1991, ISBN 0-937175-73-0.
POSIX.1b IEEE Std 1003.1b-1993 (POSIX.1b standard) describing
real-time facilities for portable operating systems,
aka ISO/IEC 9945-1:1996, as elucidated in "Programming for
the real world - POSIX.4" by Bill O. Gallmeister (O'Reilly
& Associates, Inc. ISBN 1-56592-074-0).
SUS, SUSv2 Single Unix Specification. Developed by X/Open and The
Open Group. See also http://www.UNIX-systems.org/version2/
4.3BSD The 4.3 distribution of Berkeley Unix.
4.4BSD 4.4BSD was upward-compatible from 4.3.
V7 Version 7, the ancestral Unix from Bell Labs.
intro - Introduction to library functions
-----------------------------------------
This chapter describes all library functions excluding the library
functions described in chapter 2, which implement system calls. There
are various function groups which can be identified by a letter which
is appended to the chapter number:
(3C) These functions, the functions from chapter 2 and from
chapter 3S are contained in the C standard library libc, which
will be used by cc(1) by default.
(3S) These functions are parts of the stdio(3) library. They are
contained in the standard C library libc.
(3M) These functions are contained in the arithmetic library libm.
They are used by the f77(1) FORTRAN compiler by default, but not
by the cc(1) C compiler, which needs the option -lm.
(3F) These functions are part of the FORTRAN library libF77. There are
no special compiler flags needed to use these functions.
(3X) Various special libraries. The manual pages documenting their
functions specify the library names.
Date: 20050522
Source: http://www.die.net/doc/linux/man/