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getrusage
For a detailed description about the values returned by
getrusage() please consult your usual C programming
documentation about getrusage() and also the header file
sys/resource.h. The $ru_who argument is either
RUSAGE_SELF (the current process) or RUSAGE_CHILDREN (all
the child processes of the current process). On some
(very few) systems (those supporting both getrusage() and
the POSIX threads) there is also RUSAGE_THREAD. The
BSD::Resource supports the _THREAD flag if it is present
but understands nothing about the POSIX threads
themselves.
Note 1: officially HP-UX 9 does not support getrusage() at
all but for the time being, it does seem to.
Note 2: Solaris claims in sys/rusage.h that the ixrss and
the isrss fields are always zero.
getrlimit
Processes have soft and hard resource limits. At soft
limit they receive a signal (XCPU or XFSZ, normally) they
can trap and handle and at hard limit they will be
ruthlessly killed by the KILL signal. The $resource
argument can be one of
RLIMIT_CPU RLIMIT_FSIZE
RLIMIT_DATA RLIMIT_STACK RLIMIT_CORE RLIMIT_RSS
RLIMIT_NOFILE RLIMIT_OPEN_MAX
RLIMIT_AS RLIMIT_VMEM
The last two pairs (NO_FILE, OPEN_MAX) and (AS, VMEM) mean
the same, the former being the BSD names and the latter
SVR4 names. Two meta-resource-symbols might exist
RLIM_NLIMITS
RLIM_INFINITY
NLIMITS being the number of possible (but not necessarily
fully supported) resource limits, INFINITY being useful in
setrlimit().
NOTE: the level of 'support' for a resource varies. Not
all the systems
a) even recognise all those limits
b) really track the consumption of a resource
c) care (send those signals) if a resource limit get exceeded
Again, please consult your usual C programming
documentation.
One notable exception: officially HP-UX 9 does not support
getrlimit() at all but for the time being, it does seem
to.
getpriority
The priorities returned by getpriority() are
[PRIO_MIN,PRIO_MAX]. The $which argument can be any of
PRIO_PROCESS (a process) PRIO_USER (a user), or PRIO_PGRP
(a process group). The $pr_who argument tells which
process/user/process group, 0 signifying the current one.
setrlimit
A normal user process can only lower its resource limits.
Soft or hard limit RLIM_INFINITY means as much as
possible, the real limits are normally buried inside the
kernel.
setpriority
The priorities handled by setpriority() are
[PRIO_MIN,PRIO_MAX]. A normal user process can only lower
its priority (make it more positive).
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