jobs

Overview

The jobs command displays active jobs in the current shell session. It shows background processes, suspended jobs, and their status, making it essential for job control in shell environments.

Syntax

jobs [options] [job_spec...]

Common Options

Option Description
-l List process IDs
-n Show only jobs that have changed status
-p Show only process IDs
-r Show only running jobs
-s Show only stopped jobs
-x command Replace job specs with PIDs

Job States

State Description
Running Job is executing
Stopped Job is suspended
Done Job completed successfully
Exit Job exited with error
Terminated Job was killed

Key Use Cases

  1. Monitor background jobs
  2. Job control management
  3. Process status checking
  4. Shell session management
  5. Script job tracking

Examples with Explanations

Example 1: List All Jobs

jobs

Shows all active jobs in current shell

Example 2: Show Process IDs

jobs -l

Lists jobs with their process IDs

Example 3: Running Jobs Only

jobs -r

Shows only currently running jobs

Example 4: Stopped Jobs Only

jobs -s

Shows only suspended/stopped jobs

Job Control Basics

  1. Start background job:

    command &

  2. Suspend current job:

    Ctrl+Z

  3. Resume in background:

    bg %1

  4. Resume in foreground:

    fg %1

Job Specification

Format Description
%n Job number n
%string Job whose command begins with string
%?string Job whose command contains string
%% or %+ Current job
%- Previous job

Common Usage Patterns

  1. Check job status:

    jobs -l | grep Running

  2. Count active jobs:

    jobs | wc -l

  3. Find specific job:

    jobs | grep command_name

Understanding Output

Typical output format:

[1]+  Running    long_command &
[2]-  Stopped    vim file.txt
[3]   Done       make all

Components: - [1]: Job number - +: Current job - -: Previous job - Running/Stopped/Done: Job state - Command: The command being executed

Advanced Usage

  1. Show only PIDs:

    jobs -p

  2. Changed status only:

    jobs -n

  3. Execute with job replacement:

    jobs -x echo %1

Performance Analysis

  • Instant operation
  • No system resource usage
  • Shell-specific information
  • Real-time status
  • Efficient for job management

Best Practices

  1. Regular job status checking
  2. Clean up completed jobs
  3. Use job control effectively
  4. Monitor long-running processes
  5. Understand job specifications

Job Management

  1. Background a running job:

    # Ctrl+Z to suspend
bg %1  # Resume in background

  2. Foreground a background job:

    fg %1

  3. Kill a job:

    kill %1

Scripting Applications

  1. Wait for jobs to complete:

    #!/bin/bash
command1 &
command2 &
command3 &

while [ $(jobs -r | wc -l) -gt 0 ]; do
    sleep 1
done
echo "All jobs completed"

  2. Job monitoring:

    monitor_jobs() {
    while true; do
        if jobs -r | grep -q .; then
            echo "$(date): $(jobs -r | wc -l) jobs running"
        fi
        sleep 10
    done
}

Integration Examples

  1. With process management:

    # Start multiple jobs
for i in {1..5}; do
    long_task $i &
done

# Monitor progress
jobs -l

  2. Conditional job control:

    if jobs -r | grep -q "backup"; then
    echo "Backup still running"
else
    start_backup &
fi

Job Cleanup

  1. Remove completed jobs:

    jobs -n  # Shows status changes

  2. Kill all jobs:

    kill $(jobs -p)

  3. Wait for all jobs:

    wait  # Built-in command

Shell-Specific Behavior

Different shells handle jobs differently: - Bash: Full job control support - Zsh: Enhanced job control - Fish: Modern job management - Dash: Limited job control

Troubleshooting

  1. Jobs not showing up
  2. Job control disabled
  3. Shell session issues
  4. Process orphaning
  5. Job state confusion

Security Considerations

  1. Monitor background processes
  2. Clean up abandoned jobs
  3. Check for unauthorized processes
  4. Resource usage monitoring
  5. Process privilege checking

Automation Examples

  1. Parallel processing:

    #!/bin/bash
MAX_JOBS=4

process_file() {
    # Process file in background
    heavy_processing "$1" &

    # Limit concurrent jobs
    while [ $(jobs -r | wc -l) -ge $MAX_JOBS ]; do
        sleep 1
    done
}

for file in *.txt; do
    process_file "$file"
done

# Wait for all to complete
wait

  2. Job status reporting:

    report_jobs() {
    echo "Job Status Report - $(date)"
    echo "Running: $(jobs -r | wc -l)"
    echo "Stopped: $(jobs -s | wc -l)"
    echo "Total: $(jobs | wc -l)"
}