Provided by: killer_0.90-13_all bug


       killer - Background job killer


       killer [-h] [-V] [-n] [-d]


       killer is a perl script that gets rid of background jobs.  Background jobs are defined as
       processes that belong to users who are not currently logged into the machine.  Jobs can be
       run in the background (and are expempt from killer's acctions) if their scheduling
       priority has been reduced by increasing their nice(1) value or if they are being run
       through condor.  For more details, see the PACKAGE main section of this document.

       The following sections describe the perl(1) packages that make up the killer program.  I
       don't expect that the version that works for me will work for everyone.  I think that the
       ProcessTable and Terminals packages offer enough flexibility that most modifications can
       be done in the main package.

       Command line options

       -h  Tell me how to get help

       -V  Display version number

       -n  Do not kill, just print what would be killed

       -d  Enable debug output

PACKAGE ProcessTable

       Each ProcessTable object contains hashes (or associative arrays) that map various aspects
       of a job to the process ID (PID).  The following hashes are provided:

       pid2user    Login name associated with the effective UID that the process is running as.

       pid2ruser   Login name associate with the real UID that the process is running as.

       pid2uid     Effective UID that the process is running as.

       pid2ruid    Real UID that the process is running as.

       pid2tty     Terminal associated with the process.

       pid2ppid    Parent process of the process

       pid2nice    nice(1) value of the process.

       pid2comm    Command name of the process.

       Additionally, the %remainingprocs hash provides the list of processes that will be killed.

       The intended use of this package calls for readProcessTable to be called to fill in all of
       the hashes defined above.  Then, processes that meet specific requirements are removed
       from the %remainingprocs hash.  Those that are not removed are considered to be background
       processes and may be killed.

       This function creates a new ProcessTable object.


           my $ptable = new ProcessTable;

       This function (re)initializes arrays and any environment variables for external commands.
       It generally will not need to be called, as it is invoked by new().


           # Empty out the process table for reuse

       This function executes the ps(1) command to figure out which processes are running.  Note
       that it requires a SYSV style ps(1).


           # Get a list of processes from the OS

       This function looks for a large number of processes owned by one user, and assumes that it
       is someone that is using fork() for the first time.  An effective way to clean up such a
       mess is to "kill -STOP" each process then "kill -KILL" each process.

       Note this function ignores such mistakes by root.  If root is running a fork(2) bomb, this
       script wouldn't run, right?  Also, you should be sure that the number of processes
       mentioned below (490) is less (equal to would be better, right?) than the maximum number
       of processes per user.  Also, the OS should have a process limit at least a couple hundred
       higher than any individual.  Otherwise, you will have to use the power switch to get rid
       of fork bombs.

       Each time a process is sent a signal, it is logged via syslog(3C).


           # Get rid of fork bombs.  Keep track of who did it in @idiots.
           my @idiots = $ptable->cleanForkBombs();

   getUserProcessIds user
       This returns the list of process ID's where the login associated with the real UID of the
       process matches the argument to the function.


           # Find all processes owned by httpd
           my @webservers = $ptable->getUserProcessIds('httpd');

       This function returns a list of terminals in use.  Note that the format will be the same
       as given by ps(1), which will generally lack the leading "/dev/".


           # Get a list of all terminals that processes are attached to
           my @ttylist = $ptable->getUniqueTtys();

   removeProcessId pid
       This function removes pid from the list of processes to be killed.  That is, it gets rid
       of a process that should be allowed to run.  Most likely this will only be called by other
       functions in this package.


           # For some reason I know that PID 1234 should be allowed to run

   removeProcesses psfield, psvalue
       This function removes processes that possess certain traits.  For example, if you want to
       get rid of all processes owned by the user "lp" or all processes that have /dev/console as
       their controlling terminal, this is the function for you.

       psfield can be any of the following

       pid     Removes process id given in second argument.

       user    Removes processes with effective UID associated with login name given in second

       ruser   Removes processes with real UID associated with login name given in second

       uid     Removes processes with effective UID given in second argument.

       ruid    Removes processes with real UID given in second argument.

       tty     Removes processes with controlling terminal given in second argument.  Note that
               it should NOT start with "/dev/".

       ppid    Removes children of process with PID given in second argument.

       nice    Removes children with a nice value equal to the second argument.

       comm    Removes children with a command name that is the same as the second argument.


           # Allow all imapd processes to run
           $ptable->removeProcesses('comm', 'imapd');

           # Be sure not to kill print jobs
           $ptable->removeProcesses('ruser', 'lp');

   removeChildren pid
       This function removes all decendents of the given pid.  That is, if the pid argument is 1,
       it will ensure that nothing is killed.


           # Be sure not to kill off any mail deliveries (assumes you have
           # written getSendmailPid()).  (Sendmail changes uid when it does
           # local delivery.)

       Condor is a batch job system that allows migration of jobs between machines (see  This ensures that condor jobs are left alone.


           # Be nice to the people that are running their jobs through condor.

   findChildProcs pid
       This function finds and returns a list of all of the processess that are descendents of a
       the PID given in the first argument.


           # Find the processes that are decendents of PID 1234
           my @procs = $ptable->findChildProcs(1234);

   getTtys user
       This function returns a list of tty's that are in use by processes owned by a particular


           # find all tty's in use by gerdts.
           my @ttylist = getTtys('gerdts');

       This function lists all the users that have active processes.


           # Get all users that are logged in
           my @lusers = $ptable->getUsers()

       This function removes all jobs that have a nice value greater than 9 (default is 0, and 10
       when running with the "nice" command without specifying nice value).


           # Allow people to run background jobs so long as they yield to
           # those with "foreground" jobs

   printProcess filehandle, pid
       This function displays information about the process, kinda like "ps | grep" would.


           # Print info about init to STDERR
           $ptable->printProcess(\*STDERR, 1);

   printProcessTable filehandle
       This function prints info about all the processes discoverd by readProcessTable.  If an
       argument is given, it should be a file handle to which the output should be printed.


           # Print the process table to stdout

           # Mail the process table to someone
           open MAIL '|/usr/bin/mail someone';

   printRemainingProcesses filehandle
       This function prints info about all the processes discoverd by readProcessTable, but not
       removed from %remainingprocs.  If an argument is given, it should be a file handle to
       which the output should be printed.


           # Print the jobs to be killed to stdout

           # Mail the jobs to be killed to someone
           open MAIL '|/usr/bin/mail someone';

       Returns a list of processes that are likely background jobs.


           # Get a list of the processes that I plan to kill
           my @procsToKill = $ptable->getRemainingProcesses();

   killAll signalNumber
       Sends the specified signal to all the processes listed.  A syslog entry is made for each
       signal sent.


           # Send all of the remaining processes a TERM signal, then a
           # KILL signal
           sleep(10);          # Give them a bit of a chance to clean up

PACKAGE Terminals

       The Terminals package provides a means for figuring out how long various users have been

       This function is used to instantiate a new Terminals object.


           # Get a new Terminals object.
           my $term = new Terminals;

       This function figures out who is on the system and how long they have been idle for.  It
       will generally only be called by new().


           # Refresh the state of the terminals.

       This function returns the login of the person that is physically sitting at the machine.


           # Print out the login of the person on the console
           printf "%s is on the console\n", $term->showConsoleUser();

   initializeTty terminal statparts
       This initializes internal structures for the given terminal.

   getX11IdleTime user
       Figure out how long a user has been idle in X11.  Return the seconds of idle time.

   getIdleTime user
       Figure out how long a user has been idle.  This is accomplished by examining all terminals
       that the user owns and returns the amount of time since the most recently accessed one was
       used.  Additionally, if the user is at the console it is possible that he/she is not
       typing, yet is quite active with the mouse or typing into an application that does not use
       a terminal.


           # Figure out how long the user on the console has been idle
           my $consoleIdle = $term-getIdleTime($term->showConsoleUser());

       Prints to stdout who is on what terminal and how long they have been idle.  Only useful
       for debugging.


           # Take a look at the contents of structures in my
           # Terminals object


       The main package is the version used on the Unix workstations at the University of
       Wisonsin's Computer-Aided Engineering Center (CAE).  I suspect that folks at places other
       than CAE will want to do things slightly differently.  Feel free to take this as an
       example of how you can make effective use of the processTable and Terminals packages.

   Configuration options
       $forkadmin  Email address to notify of fork bombs

       $killadmin  Email address to notify of run-of-the-mill kills

       $fromaddr   Who do email messages claim to be from?

                   Email address to notify when jobs will not die

       @validusers These are the folks that you should never kill off

       $minuid     Do not kill processes of users with uid lower than this value.

                   The maximum number of seconds that a user can be idle without being classified
                   as having "background" jobs.

       If I am a user really trying to avoid a background job killer, I would likely include a
       signal handler that would wait for signal 15.  When I saw it, I would fork causing the
       parent to die and the child would continue on to do my work.

       Assuming that everyone thinks like me, I figure that I will need to make at least two
       complete passes to clear up the bad users.  The first pass is relatively nice (sends a
       signal 15, followed a bit later by a signal 9).  A well-written program will take the
       signal 15 as a sign that it should clean up and then shut down.  When a process gets a
       signal 9, it has no choice but to die.

       The second pass is not so nice.  It finds all background processes, sends them a signal 23
       (SIGSTOP), then a signal 9 (SIGKILL).  This pretty much (but not absolutely) guarantees
       that processes are unable to find a way around the background job killer.

       This function gathers information from the Terminals and ProcessTable packages, then based
       on that information decides which jobs should be allowed to run.  Specifically it does the

       · Instantiates new ProcessTable and Terminals objects.  Note that Terminals::new fills in
         all the necessary structures to catch users that have logged in between calls to

       · Reads the process table

       · Removes condor processes and condor jobs from the list of processes to be killed.

       · Removes all jobs belonging to all users in the configuration array @validusers from the
         list of processes to be killed.

       · Removes all nice(1) jobs from the list of jobs to be killed.

       · Removes all jobs belonging to users where the user has less than $maxidletime idle time
         on at least one terminal.  Additionally, jobs associated with ttys that are owned by
         users that have less than $maxidletime idle time on at least one terminal are preserved.
         This makes it so that if luser uses su(1) to gain the privileges of boozer, processes
         owned by boozer will not be killed.

       · Removes all processes of users with uid lower than the $minuid value.

       · Finally, the process table and terminal objects are returned.


       There is a small window of opportunity for a user that reaches $maxidletime in the middle
       of this script to get unfair treatment.  This could probably be reconciled by shaving some
       time off of maxidletime for the second call to main::gatherInfo.

       It is still possible to get around the background job killer by having a lot of proceses
       that watch each other to be sure that they are still responding (have not yet gotten a
       signal 23).  As soon as a stopped process is found, the still running process could
       fork(), thus leaving a background process that is not going to be killed.

       Different operating systems have different notions of nice values.  Some go from -20 to
       +19.  Some go from 0 to 39.  Solaris and HP-UX (using System V ps command) report nice
       values between 0 and 39.

       It is bad to assume that all systems that run this have the same number of processes per
       user.  The script should ask the OS how many processes normal (non-root) users can run.


       The configuration is quite minimalistic.  It should be made possible to have per-host
       configuration directives so that you can, for instance, allow certain people to run
       background jobs on certain hosts.

       People that really care about finding habitual offenders will probably want to have a way
       to add entries to a database and flag those that pop up too often.

       Thoroughly test on more operating systems.  A very close relative of this code has
       performed well on about 60 Solaris 2.5.1 machines.  It has been lightly tested on HP-UX
       10.20 as well.

       Make mailing to someone optional.  If you have a lot of workstations killing off boring
       stuff all the time, too much meaningless mail traffic is generated.

       If you plan to run this on a machine that runs special processes like a POP or IMAP
       server, it would be handy to be able to check multiple conditions easily.  Perhaps

           $ptable->removeProcesses( { comm => 'imapd',
                                       parentComm => 'inetd',
                                       parentUser => 'root' } );

       This would make it so that people don't rename the crack binary imapd to escape the wrath
       of killer.


       This program is released under the terms of the General Public License (GPL) version 2.
       The the file COPYING with the distribution.  If you have lost your copy, you can get a new
       one at  In particular remember that this code is
       distributed for free without warranty.

       If you make use of this code, please send me some email.  While I am open to suggestions
       to improvement, I by no means guarantee that I will implement them.


       nice(1) perl(1) ps(1) su(1) who(1) fork(2) signal(5)


       killer was written by Mike Gerdts,

                                            2018-06-08                                  KILLER(1)