Thursday, December 01, 2016

Oracle Linux – short tip #1 – using apropos

It happens to everyone, especially on Monday mornings, you suddenly cannot remember a command which normally is at the top of your head and you used a thousand times. The way to find the command you are looking for while using Linux is making use of the apropos command. apropos  searches  a set of database files containing short descriptions of system commands for keywords and displays the result on the standard output.

As an example, I want to do something with a service however not sure which command to use or where to start researching for it. We can use apropos to take a first hint as shown below:

[root@localhost ~]# apropos "system service"
chkconfig            (8)  - updates and queries runlevel information for system services
[root@localhost ~]#

As another example, I want to do something with utmp and I want to know which commands would be providing me functionality to work with utmp. I can use the below apropos command to find out.

[root@localhost ~]# apropos utmp
dump-utmp            (8)  - print a utmp file in human-readable format
endutent [getutent]  (3)  - access utmp file entries
getutent             (3)  - access utmp file entries
getutid [getutent]   (3)  - access utmp file entries
getutline [getutent] (3)  - access utmp file entries
getutmp              (3)  - copy utmp structure to utmpx, and vice versa
getutmpx [getutmp]   (3)  - copy utmp structure to utmpx, and vice versa
login                (3)  - write utmp and wtmp entries
logout [login]       (3)  - write utmp and wtmp entries
pututline [getutent] (3)  - access utmp file entries
setutent [getutent]  (3)  - access utmp file entries
utmp                 (5)  - login records
utmpname [getutent]  (3)  - access utmp file entries
utmpx.h [utmpx]      (0p)  - user accounting database definitions
wtmp [utmp]          (5)  - login records
[root@localhost ~]#

It is not the best solution and you have to be a bit creative in understanding how the string apropos uses could be defined however, in general it can be a good start when looking for a command while using Linux. 
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