Background Jobs

Run processes without blocking the terminal.

Source: src/execution/jobs.f90, src/execution/executor.f90:269-277, src/execution/builtins.f90:778-927

Running in Background

Append & to run a command in the background:

sleep 60 &
# [1] 12345
# Shell prompt returns immediately

The shell prints:

• [1] - Job number
• 12345 - Process ID

Listing Jobs

Use jobs to list all jobs:

sleep 100 &
sleep 200 &
jobs
# [1]-  Running                 sleep 100 &
# [2]+  Running                 sleep 200 &

Jobs Options

jobs         # List all jobs
jobs -l      # Include PIDs
jobs -p      # Show only PIDs

Source: builtins.f90:778-791

Job Specification

Reference jobs by number or pattern:

vim file.txt &
./longscript.sh &
fg %vim            # Brings vim to foreground
fg %?script        # Brings longscript to foreground

Source: builtins.f90:796-854

Foreground and Background

fg - Foreground

Bring a job to the foreground:

./script.sh &
# [1] 12345
fg %1              # Bring to foreground
# ./script.sh continues in foreground

Without arguments, fg uses the current job:

fg                 # Same as fg %%

Source: builtins.f90:856-890

bg - Background

Resume a stopped job in the background:

vim file.txt
# Press Ctrl+Z
# [1]+  Stopped                 vim file.txt

bg %1
# [1]+ vim file.txt &

Source: builtins.f90:892-927

Suspending Jobs

Press Ctrl+Z to suspend the foreground job:

sleep 1000
# Press Ctrl+Z
# [1]+  Stopped                 sleep 1000

The job receives SIGTSTP and stops. Use fg to resume in foreground or bg to resume in background.

Source: jobs.f90:225-259 - suspend_job()

Waiting for Jobs

wait - Wait for Completion

Wait for background jobs to finish:

# Wait for all background jobs
./job1.sh &
./job2.sh &
wait
echo "All done"

# Wait for specific job
./longrun.sh &
wait %1
echo "longrun finished with status $?"

# Wait for specific PID
./task.sh &
pid=$!
wait $pid

Source: builtins.f90:1286-1345

$! - Last Background PID

./background.sh &
echo "Started PID $!"
wait $!

Job Completion Notification

When a background job completes, fortsh notifies you at the next prompt:

sleep 5 &
# [1] 12345
# ... wait 5 seconds and press Enter ...
# [1]+  Done                    sleep 5

Source: jobs.f90:94-112 - notify_job_status()

Process Groups

Background jobs run in their own process group. This allows:

• Sending signals to the entire job
• Terminal control management
• Job state tracking

Source: executor.f90:147-159, jobs.f90:114-178

Job Table

Jobs are tracked in shell%jobs array:

type :: job_t
  integer :: job_id
  integer(c_pid_t) :: pgid
  integer(c_pid_t), allocatable :: pids(:)
  character(len=256) :: command_line
  integer :: state          ! JOB_RUNNING, JOB_STOPPED, JOB_DONE
  logical :: foreground
end type

Source: types.f90:168-177

Killing Jobs

Send signals to jobs:

sleep 1000 &
kill %1              # SIGTERM (default)
kill -KILL %1        # SIGKILL (force)
kill -9 %1           # Same as above
kill -STOP %1        # Suspend job
kill -CONT %1        # Resume job

Negative PIDs target process groups:

kill -- -$pgid       # Kill entire process group

Source: builtins.f90:1139-1283

Common Patterns

Run and Detach

nohup ./server.sh > server.log 2>&1 &
disown %1
# Server continues even after logout

Parallel Processing

for file in *.txt; do
    process_file "$file" &
done
wait
echo "All files processed"

Background with Output

# Redirect output to avoid terminal clutter
./noisy.sh > output.log 2>&1 &

Check on Long Jobs

./compile.sh &
pid=$!

# Check periodically
while kill -0 $pid 2>/dev/null; do
    echo "Still running..."
    sleep 10
done
echo "Done!"

Limitations

• Maximum jobs: Defined by MAX_JOBS constant
• Job numbers are reused after completion
• Pipelines run as a single job (all processes in same group)