Scheduled Execution

In addition to the standard UNIX mechanisms for scheduling the time at which a program will be executed, the shell provides its own internal scheduling mechanisms. The sched and commands can be used to run a process at some future time.

[%%job ]

Puts the specified jobs into the background. Job may be a number, a string, '', '%', '', or '-'.

Example: Suppose you're running a long job and you get bored waiting on it. You don't want to stop it because it has to be run, but you want your terminal back; therefore,

1. Use the following key sequence: To suspend the job,

<Ctrl>+Z

2. To get the command's job number, use the following command:

jobs

3. To restart the job in the background, use the following command:

bg %1

exec command

Executes the specified command in place of the current shell. Note that for any command other than another shell, this is effectively a logout.

Example: To terminate your current shell and replace it with tcsh, use

exec /bin/tcsh

[%%job ]

Brings the specified jobs into the foreground. Recalls that job numbers are displayed by using the jobs command.

Example: To bring job 3 into the foreground, use

fg %3

hup

[command]

Runs the specified command in such a way that it will exit upon receiving a hangup signal. The benefit of running a command with hup is that the command will be sent a hangup signal if the parent shell exits.

Example: To run the command update_database in such a way that it will receive a hangup signal if the parent shell exits while it is running, use

hup update_database

jobs

[-l]

Lists the active jobs. The -l option includes process ids in the listing.

Example: To list the currently active jobs, together with their process id's, use

jobs -l

kill

[-signal] %%job|pid

kill-l

Sends a signal to the specified job or process, thereby killing it. Some of the more useful values for signal are

Name	Value	Effect
KILL	9	Should kill any process immediately and ungracefully.
QUIT	2	Tells the process to quit what it's doing and then die.
HUP		Politely asks the process to tidy up and then die.

To obtain complete listing of the symbolic names of the possible signals that can be generated with the l option, use

kill l

The possible signals are defined in /usr/include/signal.h.

Example: To forcefully demand that job 3 die immediately, use

kill -KILL %3

limit

[-h] [resource [maximum-use]]

Limits the consumption of the specified resource by the current process and each process it creates to not individually exceed maximum use. If no value for maximum use is given, it will display the current value

Resource may be one of
cputime	Amount of CPU time, in seconds, used by each process.
filesize	Size of largest file that can be created.
datasize	Maximum growth of the datastack region beyond end of program text.
stacksize	Maximum size of the automatically extended stack region.
coredumpsize	Size of the largest core dump.
memoryuse	Upper limit on the amount of physical memory a process may have allocated to it.

The maximum-use value may be given as a (floating point or integer) number followed by a scale factor. For all limits other than cputime the default scale is 'k' or 'kilobytes' (1024 bytes); a scale factor of 'm' or 'megabytes' may also be used. For cputime the default scaling is 'seconds', while 'm' for minutes or 'h' for hours, or a time of the form 'm:s' giving minutes and seconds may be used.