Job Control Builtins

bg

bg [jobspec ...]

Resume each suspended job jobspec in the background, as if it had been started with ‘&’. If jobspec is not supplied, the shell uses its notion of the current job. bg returns zero unless it is run when job control is not enabled, or, when run with job control enabled, any jobspec was not found or specifies a job that was started without job control.

fg

fg [jobspec]

Resume the job jobspec in the foreground and make it the current job. If jobspec is not supplied, fg resumes the current job. The return status is that of the command placed into the foreground, or non-zero if run when job control is disabled or, when run with job control enabled, jobspec does not specify a valid job or jobspec specifies a job that was started without job control.

jobs

jobs [-lnprs] [jobspec]
jobs -x command [arguments]

The first form lists the active jobs. The options have the following meanings:

-l

List process IDs in addition to the normal information.

-n

Display information only about jobs that have changed status since the user was last notified of their status.

-p

List only the process ID of the job’s process group leader.

-r

Display only running jobs.

-s

Display only stopped jobs.

If jobspec is supplied, jobs restricts output to information about that job. If jobspec is not supplied, jobs lists the status of all jobs. The return status is zero unless an invalid option is encountered or an invalid jobspec is supplied.

If the -x option is supplied, jobs replaces any jobspec found in command or arguments with the corresponding process group ID, and executes command, passing it arguments, returning its exit status.

kill

kill [-s sigspec] [-n signum] [-sigspec] id [...]
kill -l|-L [exit_status]

Send a signal specified by sigspec or signum to the processes named by each id. Each id may be a job specification jobspec or process ID pid. sigspec is either a case-insensitive signal name such as SIGINT (with or without the SIG prefix) or a signal number; signum is a signal number. If sigspec and signum are not present, kill sends SIGTERM.

The -l option lists the signal names. If any arguments are supplied when -l is supplied, kill lists the names of the signals corresponding to the arguments, and the return status is zero. exit_status is a number specifying a signal number or the exit status of a process terminated by a signal; if it is supplied, kill prints the name of the signal that caused the process to terminate. kill assumes that process exit statuses are greater than 128; anything less than that is a signal number. The -L option is equivalent to -l.

The return status is zero if at least one signal was successfully sent, or non-zero if an error occurs or an invalid option is encountered.

wait

wait [-fn] [-p varname] [id ...]

Wait until the child process specified by each id exits and return the exit status of the last id. Each id may be a process ID pid or a job specification jobspec; if a jobspec is supplied, wait waits for all processes in the job.

If no options or ids are supplied, wait waits for all running background jobs and the last-executed process substitution, if its process id is the same as $!, and the return status is zero.

If the -n option is supplied, wait waits for any one of the ids or, if no ids are supplied, any job or process substitution, to complete and returns its exit status. If none of the supplied ids is a child of the shell, or if no arguments are supplied and the shell has no unwaited-for children, the exit status is 127.

If the -p option is supplied, wait assigns the process or job identifier of the job for which the exit status is returned to the variable varname named by the option argument. The variable, which cannot be readonly, will be unset initially, before any assignment. This is useful only when used with the -n option.

Supplying the -f option, when job control is enabled, forces wait to wait for each id to terminate before returning its status, instead of returning when it changes status.

If none of the ids specify one of the shell’s an active child processes, the return status is 127. If wait is interrupted by a signal, any varname will remain unset, and the return status will be greater than 128, as described above (see Signals). Otherwise, the return status is the exit status of the last id.

disown

disown [-ar] [-h] [id ...]

Without options, remove each id from the table of active jobs. Each id may be a job specification jobspec or a process ID pid; if id is a pid, disown uses the job containing pid as jobspec.

If the -h option is supplied, disown does not remove the jobs corresponding to each id from the jobs table, but rather marks them so the shell does not send SIGHUP to the job if the shell receives a SIGHUP.

If no id is supplied, the -a option means to remove or mark all jobs; the -r option without an id argument removes or marks running jobs. If no id is supplied, and neither the -a nor the -r option is supplied, disown removes or marks the current job.

The return value is 0 unless an id does not specify a valid job.

suspend

suspend [-f]

Suspend the execution of this shell until it receives a SIGCONT signal. A login shell, or a shell without job control enabled, cannot be suspended; the -f option will override this and force the suspension. The return status is 0 unless the shell is a login shell or job control is not enabled and -f is not supplied.

When job control is not active, the kill and wait builtins do not accept jobspec arguments. They must be supplied process IDs.