Notes for the ps utility
========================

ps needs to associate /dev device names with dev_t device numbers in order
to print the controlling terminal devices. It does this by examining files
in /dev with stat(2). To accelerate this process, ps normally keeps a cache
file; the data in this file is not secret (it can be collected by any user
by examining /dev himself), but its integrity must be protected. ps thus
normally runs set-user-ID and creates the cache file with its effective
user ID. ps should be run with the credentials of either root or another
trusted user ID; it does not need privilege otherwise on Linux or Solaris
and can be configured in /etc/default/ps to switch to the real user ID
after creating the cache file. The location, permission mode, and group
ownership of the cache file can also be changed in /etc/default/ps (see
the text of that file for details).

It is also possible to disable the cache file by removing -DUSE_PS_CACHE
from Makefile.mk, and regenerating the Makefile and rebuilding ps after
doing so. If no cache file is used, ps does not need to run set-user-ID
on Linux and Solaris.

On (native) Open UNIX, ps needs root privileges to read execution times
of child processes, and effective user and group IDs. It will thus be
limited in functionality unless it runs set-user-ID to root, especially
for the SUSv2 version which uses effective user IDs for the -u option
and prints them in the UID column. With the Open UNIX LKP, no privileges
are necessary, just as on Linux, but some files in LKP /proc contain
weird values, causing ps to print weird output.

On FreeBSD, ps needs privileges for completely correct operation because
some information it has to read (e. g. process flags, priority) is not
available with /proc, but only by examining /dev/kmem with the kvm library.

The System V-style ps utility and the BSD-style version are two separate
binaries with this toolchest. Moreover, the BSD-style version does not
accept options without a preceding '-' (original BSD implementations do,
but not /usr/ucb/ps on System V which was the model implementation for
this version). If you like the ps utility to switch to BSD-style mode
if the first argument does not start with '-', as procps v2 does, use
a shell script like the following:

	case $1 in
	-*|'')
		PATH=/usr/5bin:$PATH
		exec ps ${@+"$@"}
		;;
	[0-9]*)
		PATH=/usr/ucb:$PATH
		exec ps "$@"
		;;
	*)
		opt=$1
		shift
		PATH=/usr/ucb:$PATH
		exec ps "-$opt" ${@+"$@"}
		;;
	esac

Of course, you will have to change the PATH assignments if you installed
the tools in a different location.

	Gunnar Ritter						4/6/04