nohup

Nohup is a command-line utility that allows a program to continue running after the user logs out. The name stands for "no hang up." It is commonly used to start long-running or background tasks on Unix-like systems.

It works by protecting the launched command from the hangup signal (SIGHUP) and by handling its output. If stdout or stderr are not already redirected when nohup is invoked, they are redirected to a file named nohup.out in the current working directory. When the command is started in the background (for example with an trailing ampersand), the shell typically prints the process ID of the started job. A typical invocation is: nohup mycommand arg1 > logfile.txt 2>&1 &. If you omit redirections, output may be written to nohup.out.

Use and behavior: Nohup is commonly employed for long-running tasks on remote servers where you want the process to continue after you disconnect. It is not a true daemon and does not fully detach from the terminal in all respects. It does not automatically restart the process or manage failures; for robust background services, more specialized solutions such as systemd, or terminal multiplexers like screen or tmux, are often preferred.

Availability: Nohup is widely available on Unix-like systems. On Linux it is typically provided by GNU coreutils, and it is also present on BSD variants and macOS. Users should ensure appropriate logging and consider dedicated daemon management when reliability is critical.