Run Linux Commands in the Background Without Losing Them

Why background processes exit

When a terminal session ends (e.g., network loss, screen lock, or CTRL+C), the shell sends interrupt signals to the processes attached to that session, causing them to terminate.

SIGINT : generated by CTRL+C, forces a program to stop.

SIGHUP : sent when the terminal hangs up (e.g., SSH disconnect), also terminates the process.

Method 1: Append & to the command

Placing & at the end of a command starts it in the background and makes it ignore SIGINT. The process still receives SIGHUP, so it will stop if the session is closed.

sh test.sh &

Method 2: Use nohup

nohup

(no hang‑up) runs a command immune to SIGHUP. The process continues after the SSH session ends, but CTRL+C can still stop it. Combining nohup with & protects against both signals. nohup Command [Arg ...] [&] Example that redirects output: nohup ./test.sh > out.log 2>err.log & File descriptor meanings:

0 – standard input

1 – standard output (default for > out.log)

2 – standard error

Redirect both streams to the same file:

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

Method 3: Job control ( CTRL+Z , jobs , bg , fg )

If a command was started in the foreground without &, you can pause it, move it to the background, and later resume it.

CTRL+Z : Suspends the foreground job and marks it as stopped. [1]+ Stopped ./test.sh jobs : Lists current jobs and their statuses.

jobs
[1]+  Stopped ./test.sh
[2]+  Running ./test2.sh &

bg : Resumes a stopped job in the background.

bg 1
[1]+ ./test.sh &

fg : Brings a background job to the foreground.

fg 2
./test2.sh

Method 4: GNU screen

screen

creates a virtual terminal that persists after the SSH connection drops, allowing you to detach and reattach sessions at will.

Installation

yum install screen

Typical workflow

Create a new session: screen -S yourname List sessions: screen -ls Reattach to a session: screen -r yourname Detach a session: screen -d yourname (or screen -d -r yourname to end the current session and reattach)

Terminate a session:

screen -S pid-X quit