How To Get Information on Linux

Gregg

The manpages are historically the place to go for any information about the software and utilities installed on a Linux machine. I believe that the info page seems to be the best place for newbies to go because it is so much easier to navigate, and, like manpages, it is a still a great place to get information about your system.

Suppose you want to get information about socket. You would type:

$ info socket

and you’d get a page that looks similar to a manpage but it can be navigated by using keyboard shortcuts:

q- exits back to the shell u- moves up one level n- moves to the next node on the current level p- moves to the previous node on the current level space- goes to the selected node under the cursor H- lists all of the Info commands

The commands whatis and whereis are also very useful in finding information on the system.

$ whatis printf printf (3) - formatted output conversion printf (1) - format and print data

The whatis command will list the set of manpages for a specific keyword. The keyword printf is used in the bash shell as well as the c programming language. Here you see separate pages for each usage. To view them you would specify the section number in your command to man, i.e., $ man 3 printf or man printf (which defaults to section 1). This is the same output as entering $ man -f printf.

The whereis command will list which system files reference a specified keyword or command. For example,

$ whereis socket socket: /usr/man/man7/socket.7.gz /usr/man/mann/socket.n.gz /usr/man/man2/socket.2.gz $ whereis printf printf: /usr/bin/printf /bin/printf /usr/man/man3/printf.3.gz /usr/man/man1/printf.1.gz

In case you aren’t really sure of what you’re looking for you can use a ‘keyword’ search to the man or apropos commands which will use the keyword you enter as a regex (regular expression) to find all of the matches throughout the manpages:

$ man -k printf aa_printf (3) - print text to AA-lib output buffers. asprintf (3) - print to allocated string ber_printf (3) - OpenLDAP LBER simplified Basic Encoding Rules library routines f... BIO_printf (3) - formatted output to a BIO BIO_snprintf (3) - formatted output to a BIO BIO_vprintf (3) - formatted output to a BIO BIO_vsnprintf (3) - formatted output to a BIO buffer_printf.c (3) - Buffer management functions. curl_mprintf (3) - formatted output conversion dprintf (3) - formatted output conversion format (n) - Format a string in the style of sprintf fprintf (3) - formatted output conversion etc...

In case you are interested, the manpages are broken down into different sections as listed here:

1 General Commands 2 System Calls and Error Numbers 3 C Libraries 3p perl 4 Devices and device drivers 5 File Formats and config files 6 Game instructions 7 Miscellaneous information 8 System maintenance 9 Kernel internals