How to Keep Linux Processes Running After SSH Disconnects

Signal behavior of SSH sessions

When a terminal is closed, the network drops, or CTRL+C is pressed, the shell sends signals to the processes attached to that session. Two signals are relevant:

SIGINT – generated by CTRL+C; it requests a graceful termination of the foreground process.

SIGHUP – sent when the controlling terminal disappears (e.g., SSH disconnect, screen lock, or terminal close). Processes that remain attached to the session receive this “hang‑up” signal and typically exit.

Understanding these signals is essential for keeping long‑running jobs alive after an SSH disconnect.

1. Running a command in the background with &

Appending & to a command starts it as a background job. The job no longer receives SIGINT from CTRL+C, but it still inherits the controlling terminal and will receive SIGHUP if the session ends.

sh test.sh &

2. Using nohup to ignore SIGHUP

nohup

(no hang‑up) detaches a command from the controlling terminal. It sets the signal handler for SIGHUP to “ignore”, allowing the process to continue after the SSH session ends. CTRL+C (SIGINT) still terminates the process, so nohup is often combined with & for full resilience.

Basic syntax: nohup Command [Arg …] [&] Typical redirection example (stdout to out.log, stderr to err.log):

nohup ./test.sh > out.log 2> err.log &

File descriptor meanings:

0 – standard input ( stdin)

1 – standard output ( stdout) – default redirection is 1> 2 – standard error ( stderr)

To merge stderr into stdout:

nohup ./test.sh > out.log 2>&1 &

3. Job control primitives

If a command is started in the foreground, you can manipulate it with the following built‑in shell controls:

CTRL+Z – suspends the foreground job and places it in the stopped state.

jobs – lists all current jobs with their status and job numbers.

bg %n – resumes a stopped job %n in the background.

fg %n – brings a background (or stopped) job %n to the foreground.

Example workflow:

# Start a foreground job

./test.sh

# Suspend it

CTRL+Z

# Verify job list

jobs

# Output (example)

[1]+  Stopped                 ./test.sh

# Resume in background

bg %1

# Bring back to foreground

fg %1

4. Persistent sessions with screen

GNU Screen

creates a virtual terminal that remains alive independently of the SSH connection. Processes started inside a screen session continue to run even if the network drops, because the screen server maintains the controlling pseudo‑terminal.

Installation

yum install screen

Typical workflow

Create a new session: screen -S <session_name> List existing sessions: screen -ls Detach from the current session (leaving it running): screen -d <session_name> Reattach to a detached session: screen -r <session_name> Terminate a session: screen -S <session_name> quit Example usage:

# Start a detached session named myjob

screen -S myjob

# Inside the screen, launch a long‑running command

nohup ./long_task.sh > task.log 2>&1 &

# Detach (Ctrl+A then D) and safely disconnect SSH

# Later, reconnect and reattach

screen -r myjob