3. On Line Help

Contents of this section

When you are looking for general help on commands and error messages, the best place to start is right on your system.

3.1 Man Pages

Most every command on your system has an associated ``man'' page. This is documentation that you can get to instantly should you have questions or problems. If you were having trouble with the command ls, you could enter man ls. This will bring up the man page for ls. The man page is viewed through the less program, so all of the options to less will work while in a man page. Some important key strokes are:

Sometimes viewing man pages isn't too friendly on line. Providing you have a working printer, you can print man pages as well. If you don't have postscript printing capability and just want to print ASCII, you can print man pages with man COMMAND | groff -mandoc -Tascii | lpr. If you do have a postscript printer, you will probably want to print with man COMMAND | groff -mandoc | lpr. In both of those commands substitute ``COMMAND'' for the command you are trying to get help for.

Also, sometimes things have more than one man page. Here is a table of what is located where:

Section     Contents
-------     ----------------
   1        user commands
   2        system calls
   3        library calls
   4        devices
   5        file formats
   6        games
   7        miscellaneous
   8        system commands
   9        kernel internals

So, let's say that you want to see the man page for swapon. You do man swapon. You will actually get the man page for the system call swapon(2), which is the function you use in a C program to turn swap on. Unless you are writing your own program to do it, this probably isn't what you want. So, using the chart above, you can see that what you want is probably a ``system command'' and is located in section 8. You can then do man 8 swapon. All of this is because man searches the man directories in order, and then returns when it finds the first match.

You can also search the man pages for strings. You do this using man -k string_to_search_for. This won't work, however, unless the database is created. Under Red Hat, this gets done by a cron job overnight. If you don't leave your system on overnight you won't have the database. If that is the case, just run:

/usr/sbin/makewhatis /usr/man /usr/X11R6/man

Note: This must be done as root. Once you've done that, you could do man -k swapon. That would return:

# man -k swapon
swapon, swapoff (2)  - start/stop swapping to file/device
swapon, swapoff (8)  - enable/disable devices and files for paging and swapping
swapon, swapoff (2)  - start/stop swapping to file/device
swapon, swapoff (8)  - enable/disable devices and files for paging and swapping

So you can see that there are pages in section 2 and 8 both referring to swapon (and swapoff in this case).

3.2 Package Documentation

Many packages of software have READMEs and other documentation as part of the source package. We have come up with a standard place to install those documents for you so that you don't have to install the sources to look at the documents. All of those documents are stored in subdirectories of /usr/doc. The subdirectory depends on the package. Each package that has extra documentation will create a directory called packagename-version-releasenumber. For example, the tin package might be version 1.22 and release number 2. The path to its documentation would be /usr/doc/tin-1.22-2.

For the most part, the documents in this directory are ASCII. You can usually for them with more filename or less filename.

This is nice, but what if you want to see if there is documentation for a specific command or file and you don't know the package it came from? It doesn't matter! You can simply do:

rpm -qdf /etc/sendmail.cf

This will report all the documentation from the package containing the file /etc/sendmail.cf. Commands like this are covered more in depth in the RPM-HOWTO, most likely available wherever you got this document.

Also, what if it's a command you need help with and the man page isn't good? You could do something like:

rpm -qdf `which COMMAND`

Again, where ``COMMAND'' is the actual command you need help with. This will only work when the command is on your path.

3.3 HOWTOs and FAQs

Most of the contents of the Linux Documentation Project (LDP) are available in /usr/doc on your system.

/usr/doc/HOWTO contains the ASCII versions of all the available HOWTOs at the time we pressed the CD-ROM. They are gzipped, so you will have to use gunzip to unzip them or you will have to use something like zcat HAM-HOWTO.gz | more. The latter will work, but is a bit less flexible than unzipping and then using more. It also requires more disk space unless you re-gzip the document when done.

/usr/doc/HOWTO/mini contains the ASCII versions of all the available mini-HOWTOs. They are not compressed and can be viewed with more or less.

/usr/doc/HTML contains the HTML versions of all the HOWTOs and the _Linux Installation and Getting Started_ guide. To view things here, just use a WWW browser (like lynx or Mosaic). You would do something like:

cd /usr/doc/HTML
lynx index.html

/usr/doc/FAQ contains ASCII version (and some HTML versions) of some popular FAQs, including the RedHat-FAQ. All of them can be viewed using more or less.

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