trying to understand crontab entry for sysstat

[geppetto1]

I'm trying to understand a crontab entry for sysstat. The entry is from /etc/cron.d/sysstat:

*/10 * * * * root command -v debian-sa1 > /dev/null && debian-sa1 1 1


What I know:

*/10 * * * * - execute command every 10 minutes
&& - we're executing multiple commands consecutively
debian-sa1 1 1 - execute 'debian-sa1 1 1' executes 'sa1' and passes '1 1' to sa1 as options.

also, from the debian-sa1 file - Debian sa1 helper which is run from cron.d job, not to needlessly fill logs (see Bug#499461). I'm guessing that the bug is responsible for the existence of 'debian-sa1'

What I don't understand:

root command -v debian-sa1 > /dev/null

...could be that ' debian-sa1 > /dev/null' is the first command, but then I don't understand 'root command -v'

...more likely that 'root command -v debian-sa1 > /dev/null' is the first command, but then I still don't understand 'root command -v'

maybe what I'm asking is - what is the purpose of 'root command -v' ?

My knowledge is both dated (SVR4) and faded so any help would be appreciated. Hopefully I picked the proper forum for a question of this type.

Thank you and regards.

[gmargo]

*/10 * * * * root command -v debian-sa1 > /dev/null && debian-sa1 1 1
what is the purpose of 'root command -v' ?

Referencing the crontab(5) man page: for a system cron file, the columns are:


# m h dom mon dow user command
so "root" is the user id under which the command is run.

Referencing the dash(1) man page: the shell builtin command named "command" has this syntax for -v:


command [-p] [-v] [-V] command [arg ...]
Execute the specified command but ignore shell functions when searching for it. (This is useful when you have a shell function with the same name as a builtin command.)
...
-v Do not execute the command but search for the command and print the absolute pathname of utilities, the name for builtins or the expansion of aliases.
So "command -v debian-sa1" says "find the command named 'debian-sa1' on the $PATH (which includes /usr/lib/sysstat) and print the full pathname. Actually the pathname is ignored ("> /dev/null") and only the return code is checked ("&&"). And if the return code is zero, which means the command was found, then it is run ("debian-sa1 1 1").

[geppetto1]

Thank you for your reply and detailed explanation of the command!

The links to the crontab and dash man pages are really appreciated. I had referenced some web pages describing the crontab (not the man page) and had not seen a reference to the user id.

I never would have found the dash man page without your assistance and am not sure I would have understood the command without your explanation.

Thank you.