Computer Science › Operating Systems

Exit Code

The number a program returns when it ends; 0 means success.

Also known as: exit status, return code, status code of a process

An exit code is the small number a program hands back to the operating system when it ends. By convention, 0 means success, and any non-zero value means some kind of failure. Scripts, CI systems and schedulers use it to decide what to do next.

ls /tmp
echo $?             # 0: the last command succeeded

ls /nonexistent
echo $?             # 2: it failed

$? holds the exit code of the previous command in a shell.

Using them in scripts

if grep -q "ERROR" app.log; then        # grep exits 0 if found, 1 if not
  echo "problems found"
fi

make build && make deploy               # run deploy only if build succeeded (exit 0)
make build || echo "build failed"       # run the echo only on failure

set -e                                  # stop the script on the first failing command

In your own programs

import sys
if not config_ok:
    print("bad config", file=sys.stderr)
    sys.exit(1)             # tell the caller it failed

process.exit(1);

A program that always exits 0 hides failures from CI and cron, and a pipeline marked green when it should be red. A crash from an unhandled exception already returns non-zero.

Common conventions

Others are defined by each tool, so check its manual (getting help).

Why it matters

• CI fails a step on a non-zero code (continuous integration).
• Cron and orchestrators use it to mark runs failed and retry (cron).
• Pipes only report the last command’s code unless you set pipefail.
• Containers exit when the main process exits, and the code explains why.