.\"
.\" Copyright (c) 1986, 1994, 1996, 2000, 2002
.\"	Jeff Forys (jeffware@marjum.com).  All rights reserved.
.\"
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.\" must display the following acknowledgment: ``This product includes
.\" software developed by Jeff Forys (jeffware@marjum.com).'', (4)
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.\" derived from this software without specific prior written permission.
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.\" $Id: skill.1,v 1.21 2005/04/06 23:43:34 forys Exp $
.\"
.\" skill - send signals to processes by tty, user name, command or proc id.
.\" skill - reprioritize processes by tty, user name, command or proc id.
.\"
.TH SKILL 1 "April 6, 2005" "" "Local UNIX Programmer's Manual"
.UC 4
.SH NAME
skill, snice \- signal or reprioritize specified processes
.SH SYNOPSIS
.B skill
[\-signal] [\-afinvw] {tty user command pid}
.br
.B snice
[(\-\||\|+)priority] [\-afinvw] {tty user command pid}
.br
.B skill
\-l
.SH DESCRIPTION
.I Skill
sends the 
.I terminate
signal to a set of processes.
If a signal name (or number) preceded by a `-' is given,
that signal will be substituted for terminate.  The command
.I `skill -l'
displays a list of available signals.
.PP
.I Snice
alters the scheduling priority of selected processes.
By default, the new priority is
.I +4,
but an argument of the form `+N' (or `-N') can be used to specify
some other value.
Since the meaning of "priority" differs wildly,
.I snice
will normalize priorities to the range PRIO_MIN through PRIO_MAX;
generally `-20' is the highest priority and `+20' is the (s)lowest.
Apart from the super-user, users may only increment their priority.
An invalid priority is quietly rounded up or down to the first
acceptable value.
Where multiple scheduling classes are available,
.I snice
is only guaranteed to operate on processes in the "Time Share" class.
.PP
Options accepted by both commands are as follows:
.IP \-a
When run by an unprivileged user, processes that belong to other users
are quietly ignored.  In all mode, this internal filter is disabled.
It may be used in conjunction with the `-n' flag to display a set of
processes that match a specified criteria.  This flag has no effect
for the super-user.
.IP \-f
In fast mode, the machine-dependent code responsible for reading
processes is allowed to make decisions to improve speed at the
expense of error reporting (e.g. commands may not be displayed).
This option mainly exists to aid in killing runaway processes
on operating systems with complicated virtual memory designs.
.IP \-i
In interactive mode, the user is prompted with each process
that is a candidate for action.  Responding `y' will carry out
the stated action.  Also, a ^D at this prompt causes
.I skill
or
.I snice
to exit immediately.
.IP \-n
Display process id's but do
.I not
act on them.
.IP \-v
In verbose mode, the id of each process successfully acted
upon is displayed.  Verbose mode may be enabled by default
by setting the "\fBSKILL_VERBOSE\fP" environment variable.
.br
Alternately, when this is the only argument,
version information is displayed and the program exits.
.IP \-w
Display warning messages for unreachable processes.
.PP
All command line arguments are order independent.
.I Skill
and
.I snice
allow processes to be specified using any combination of
ttys, user names, and commands (as well as process id's).
Only processes that match something in
each category are acted upon.  An empty category
guarantees a match.  For example, `skill -HUP vi ex tty00' will
send the
.I hangup
signal to all
.I vi(1)
and
.I ex(1)
processes associated with
.I tty00.
Similarly, `snice +10 find root' will change the priority of
all
.I find(1)
processes owned by
.I root
to
.I +10.
.PP
Unprivileged users can only change their own processes so they need
.B not
specify their user name as part of the argument list.
On the other hand, the super-user should be more careful
(e.g. the command `snice -5 vi' will change the priority of 
.B every
vi(1) process on the system).
.PP
Since
.I skill
and
.I snice
categorize their arguments, there is a chance that they
will do so incorrectly (e.g. a system command is also a user
name).  Both programs try to match an argument with a
.I tty,
a
.I user name,
and a
.I process id,
before classifying it as a
.I command.
To override this, an argument can be
.B forced
to a particular type by preceding it with `-c' (command), `-u'
(user), `-t' (tty), or `-p' (process id).
As a special case, a question mark (`?') is categorized as a tty, and
will match processes without controlling ttys.
.PP
When targeting processes by command name, both
.I skill
and
.I snice
use the actual name of the binary (i.e. that which is
used for accounting purposes).  Otherwise, as processes are
permitted to change their argument vector (specifically argv[0]),
an errant program could continually change its name to avoid being
acted upon.  When targeting a process that has changed its name,
use the `-nv' options to see its actual name.  Command names may
be specified using regular expressions by enclosing them in forward
slashes.  For example, `skill -KILL /d$/' will send the
.I kill
signal to processes with names ending in "\fId\fP".
.PP
Process id's are not known beforehand, so both kernel memory and the
swap device must be searched for the required information.  Alternately,
on some systems, the "/proc" file system is examined.  When
a process fitting each category is discovered, it is immediately
acted upon (unless running in interactive or display-only mode).  Processes
must belong to the current user unless said user is the super-user.  Neither
program will ever act on itself, but everything else is fair game.
.PP
Exit status is normally 0; if the user makes a mistake, 1 is returned.
If a system error occurs, exit status is 2.
.SH "FILES"
/vmunix		system name list
.br
/dev/mem		physical memory
.br
/dev/kmem		kernel virtual memory
.br
/dev/drum		swap device
.br
/proc		process file system
.br
/dev			searched to map ttys into device numbers
.SH "SEE ALSO"
kill(1), nice(1), priocntl(1), renice(1), ps(1),
.br
kill(2), setpriority(2), signal(2), regex(3), proc(4)
.SH "AUTHOR"
Jeff Forys
.SH "CONTRIBUTORS"
David Sharnoff		Greg Earle		Christos Zoulas
.br
Gorodecki Tom		Mike Hibler		Ric Anderson
.br
Chuck L Blake		Lee Duncan		Allan E Johannesen
.br
Michael Smith		Aaron Denney		Simon Burge
.SH "BUGS"
Things change while these programs execute, occasionally
processes will be missed (the `-w' flag displays these).
.sp
Systems generally truncate command names to an OS-dependent size.
To target commands with long names, specify the truncated name or
use a regular expression.
.sp
On some operating systems, these programs are unable to investigate
processes belonging to other users.  While not a problem, this fact is
reflected in the "(but N could not be checked)" notice, which follows
the "no matching processes" message.