What does exit code 0 mean?

Exit code 0 means success — the command completed without error. By Unix convention any non-zero value indicates failure, which is why shell tests like if command; then treat 0 as true.

What does exit code 127 mean?

Exit code 127 means command not found. The shell could not locate the program in PATH, usually because of a typo, a missing binary, or PATH not including the directory. Exit code 126 is related: the file was found but is not executable.

What does exit code 137 mean?

Exit code 137 is 128 + 9, meaning the process was killed by SIGKILL (signal 9). This is frequently the Linux out-of-memory killer terminating a process, or a forced kill -9. Check memory limits and system logs.

Are exit codes the same as errno?

No. An exit code is the single byte a process returns when it finishes (0-255), reported to its parent. errno is an in-process integer set by system calls to describe the last error. A program may translate an errno into an exit code, but they are different mechanisms.

Is anything I search uploaded?

No. The exit-code table and the search run entirely in your browser, so nothing you type leaves your device.

Unix Exit Codes Reference

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This is a searchable reference for Unix and Linux process exit codes — the single byte a program returns when it finishes. It combines the POSIX convention, the special codes bash assigns (126, 127, and the 128+N “killed by signal” range), and the BSD sysexits.h registry (64–78) so you can decode an exit status from any of these worlds.

How it works

An exit status is one byte, so it ranges from 0 to 255. The shell exposes it as $? after each command. Zero means success and every other value means failure. Three layers define the meanings: POSIX reserves 0 for success and treats non-zero as error; bash assigns 126 (found but not executable), 127 (command not found), and 128 + N (terminated by signal N); and sysexits.h proposes a structured set from EX_USAGE (64) to EX_CONFIG (78) for programs that want consistent, meaningful codes. Search by number, source or keyword to find the matching entry and its explanation.

Decoding signal deaths

When a process is killed by a signal, the shell reports 128 + signal. So 130 is 128 + 2 (SIGINT, i.e. Ctrl+C), 137 is 128 + 9 (SIGKILL — often the OOM killer), 139 is 128 + 11 (SIGSEGV, a segfault), and 143 is 128 + 15 (SIGTERM). To get the signal, subtract 128 from the exit code.

Example

Reading $? after a failed command:

$ ./missing-binary
bash: ./missing-binary: No such file or directory
$ echo $?
127

Exit code 127 confirms the shell could not find the command — fix the path or install the binary. Everything in this tool runs in your browser; nothing is uploaded.