suspend - Linux

Overview

The suspend command in Linux is used to pause the execution of the current shell until it receives a signal to resume, typically through a job control command such as fg (foreground). This command is mainly used in interactive shell sessions where the user wishes to temporarily halt shell activities and then resume them later.

Syntax

The basic syntax for the suspend command is as follows:

suspend [-f]
  • -f: This option forces the suspension even if the shell is running as a login shell.

Options/Flags

  • -f (force): Use this flag to force the suspension of a login shell. Normally, suspend refuses to suspend a login shell.

Examples

  1. Simple Suspension:
    Suspend the current shell:

    suspend

    You can then return to your session by typing fg in the terminal.

  2. Forcing Suspension in Login Shell:
    If you are in a login shell and need to suspend it, use:

    suspend -f

Common Issues

  • Refusal to Suspend:
    If you try using suspend in a login shell without the -f option, it will typically refuse to suspend. The error message will be something like cannot suspend login shell. Use suspend -f to override this behavior.

  • Job Control Disabled:
    If job control is turned off in your shell, suspend may not work as expected. Make sure job control is enabled (it usually is by default in most interactive shells).

Integration

suspend can be integrated with other commands for effective job management. For example, you might use suspend in a script that monitors system resources, pausing the script execution during high load:

#!/bin/bash
# Script to monitor CPU load

load=$(cat /proc/loadavg | awk '{print $1}')

# Suspend if load average exceeds 2
if (( $(echo "$load > 2" | bc -l) )); then
    suspend
fi

# Resume once the load is normal, managed externally with `fg`
  • bg: Continues jobs that were stopped (suspended) without bringing them to the foreground.
  • fg: Brings background or suspended jobs into the foreground, resuming their execution.
  • jobs: Lists the jobs currently running or stopped in the background of the current shell.

For further reading and more in-depth discussion about job control in Bash, you can refer to the GNU Bash documentation available here.