The traditional help system for Unix is the man page. Every command (and many other files, such as configuration files) has a man page, and these man pages can be read with the man program.
would show the man page for the kill command, and the output would look like this:
KILL(1) UNIX Reference Manual KILL(1) NAME kill - terminate or signal a process SYNOPSIS kill [-signal_name] pid ... kill [-signal_number] pid ... kill [-l] DESCRIPTION The kill utility sends the TERM signal to the processes specified by the pid operand(s). Only the super-user may send signals to other users' processes. The options are as follows: -l List the signal names. -signal_name A symbolic signal name specifying the signal to be sent instead of the default TERM. The -l option displays the signal names. -signal_number A non-negative decimal integer, specifying the signal to be sent instead of the default TERM. Some of the more commonly used signals: -1 -1 (super-user broadcast to all processes, or user broadcast to user's processes) 0 0 (sh(1) only, signals all members of process group) 2 INT (interrupt) 3 QUIT (quit) 6 ABRT (abort) 9 KILL (non-catchable, non-ignorable kill) 14 ALRM (alarm clock) 15 TERM (software termination signal) Kill is a built-in to csh(1) and bash(1); they allow job specifiers of the form ``%...'' as arguments so process id's are not as often used as kill arguments. See csh(1) for details. SEE ALSO csh(1), bash(1), ps(1), kill(2), sigvec(2) HISTORY A kill command appeared in Version 6 AT&T UNIX. BUGS A replacement for the command ``kill 0'' for csh(1) users should be pro vided. BSD Experimental May 31, 1993 1
What happens when you don't know which man page to read?
There is a useful tool called apropos, which will list all of the man pages containing a keyword.
For example, if I wanted to see what man pages discussed PDF file viewers, I could use the command:
And the output on my system looks like this, showing me that I could read the man pages for gv or xpdf to find out about viewing PDF files:
cont-de (1) - PDF output from TeX cont-en (1) - PDF output from TeX cont-nl (1) - PDF output from TeX pdf2dsc (1) - generate a PS page list of a PDF document pdf2ps (1) - Aladdin Ghostscript PDF to PostScript translator pdfinitex (1) - PDF output from TeX pdflatex (1) - PDF output from TeX pdftex (1) - PDF output from TeX pdftops (1) - Portable Document Format (PDF) to PostScript converter (version 0.7a) pdftotext (1) - Portable Document Format (PDF) to text converter (version 0.7a) pdfvirtex (1) - PDF output from TeX ps2ascii (1) - Aladdin Ghostscript PostScript or PDF to ASCII translator ps2pdf (1) - Aladdin Ghostscript PostScript to PDF translator gv (1x) - a PostScript and PDF previewer xpdf (1x) - Portable Document Format (PDF) file viewer for X (version 0.7a)
You will have noticed in the example above that there is a brief summary of each man page. You can use the whatis command to display this summary line for any man page:
e2fsck (8) - check a Linux second extended file system
Both apropos and whatis can use wildcards and regular expressions, which can be very handy.
Man pages are divided up into a number of logical sections, as shown in the table below:
|1||Executable programs or shell commands|
|2||System calls (functions provided by the kernel)|
|3||Library calls (functions within system libraries)|
|4||Special files (usually found in /dev)|
|5||File formats and conventions eg /etc/passwd|
|7||Macro packages and conventions eg man(7), groff(7).|
|8||System administration commands (usually only for root)|
|9||Kernel routines [Non standard]|
This allows you to have man entries with the same name in different
sections,For example, there is a printf command, and a printf
library call (from the C library), and these are known as printf(1) and
To read these two man pages (that have the same name), specify the appropriate section:
man 1 printf man 3 printf
There is a fairly basic man page viewer for X11, called xman. It allows you to browse sections and read man pages in a formatted form:
Some related commands are groff, man2html and manpath.
Both KDE and GNOME come with fancy graphical help browsers that can read man pages.
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