Exit Codes Reference

What it is

A reference for common exit codes used by shell commands, helping you understand why a command failed.

Installation

This is a conceptual reference. No installation required.

Core Concepts

• Exit Code: A small integer returned by a command upon completion.
  • 0: Indicates successful execution.
  • Non-zero: Indicates an error or abnormal termination. The specific value often provides a clue about the nature of the error.

Commands / Usage

This section describes common exit codes and their typical meanings.

General Success

• 0
  • Meaning: Command executed successfully.

General Errors

• 1
  • Meaning: Generic error code, often used when no more specific error code is available.
  • Example: grep "nonexistent_pattern" file.txt might return 1 if the pattern is not found (though grep has specific codes for this).

Command-Specific Errors

• 2

  • Meaning: Misuse of shell builtins (e.g., exit, return).
  • Example: exit 2

• 126

  • Meaning: Command invoked cannot execute (e.g., permission denied).
  • Example: chmod 000 my_script.sh && ./my_script.sh

• 127

  • Meaning: Command not found. Often due to a typo in the command name or it not being in the system’s PATH.
  • Example: lsx (if lsx is not a command)

• 128

  • Meaning: Indicates an error in the exit status of the command itself. The actual exit code is 128 + n, where n is the signal number that terminated the process.
  • Example: If a process is terminated by signal 9 (SIGKILL), its exit code would be 128 + 9 = 137.

• 130

  • Meaning: Command terminated by Ctrl+C (SIGINT).
  • Example: Running sleep 60 and pressing Ctrl+C.

Errors from Specific Commands (Common Examples)

• grep

  • 0: One or more lines were selected.
  • 1: No lines were selected.
  • 2: An error occurred.
  • Example: grep "pattern" file.txt returns 0 if found, 1 if not found.

• find

  • 0: Successful execution.
  • Non-zero: Errors occurred during traversal (e.g., permission denied on directories).
  • Example: find /root -name "*.txt" might return non-zero if it can’t access subdirectories of /root.

• ssh

  • 0: Connection successful, command executed.
  • 255: General SSH error (authentication failure, connection refused, etc.).
  • Example: ssh user@nonexistent-host will likely return 255.

• curl

  • 0: Success.
  • 6: Couldn’t resolve host.
  • 7: Failed to connect to host.
  • 22: HTTP page not retrieved (e.g., 404 Not Found).
  • 35: SSL connect error.
  • Example: curl http://localhost:9999 (if nothing is listening) might return 7. curl http://example.com/nonexistent-page might return 22.

• rsync

  • 0: Success.
  • 1: Syntax or usage error.
  • 2: Protocol incompatibility.
  • 3: Errors selecting input/output files, dirs.
  • 4: Requested action not supported.
  • 5: Error starting client-server protocol.
  • 10: Error starting client-server protocol.
  • 11: Error in socket I/O.
  • 12: Error in file I/O.
  • 13: Error data stream.
  • 14: Errors in running rsync process.
  • 20: Error in section negotiation.
  • 21: No files found from the input.
  • 22: Error in --exclude / --include processing.
  • 23: Error in remote I/O.
  • 24: Error in --files-from generation.
  • 25: Bad exit status from rsync wrapper.
  • 30: Partial transfer due to error.
  • 35: This rsync is older than the remote rsync.
  • 45: The --local option was used together with a remote or local file name.
  • 50: Local I/O error.
  • 51: Remote path does not exist or does not created.
  • 52: Error generating temporary file name.
  • 53: Too many files to create temporary file.
  • 54: Remote file creation needs a parent directory.
  • 55: Remote directory creation needs a parent directory.
  • 56: Requested --files-from format not supported.
  • 57: Cannot stat source.
  • 58: Source not found.
  • 59: Invalid argument to --max-delete.
  • 60: Remote message was too long.
  • 61: Remote message was invalid.
  • 62: Remote message was empty.
  • 63: Checksum mismatch.
  • 64: Object not found.
  • 65: Chunk checksum mismatch.
  • 66: Object has been deleted.
  • 67: Invalid object name.
  • 68: Invalid object size.
  • 69: Invalid object modification time.
  • 70: Invalid object permissions.
  • 71: Invalid object owner/group.
  • 72: Invalid object symlink.
  • 73: Object type mismatch.
  • 74: Object name too long.
  • 75: Object name contains invalid characters.
  • 76: Object name is invalid.
  • 77: Object name is reserved.
  • 78: Object name is a directory.
  • 79: Object name is a file.
  • 80: Object name is a symlink.
  • 81: Object name is a device.
  • 82: Object name is a socket.
  • 83: Object name is a pipe.
  • 84: Object name is a FIFO.
  • 85: Object name is a hardlink.
  • 86: Object name is a special file.
  • 87: Object name is a character device.
  • 88: Object name is a block device.
  • 89: Object name is a remote file.
  • 90: Object name is a remote directory.
  • 91: Object name is a remote symlink.
  • 92: Object name is a remote device.
  • 93: Object name is a remote socket.
  • 94: Object name is a remote pipe.
  • 95: Object name is a remote FIFO.
  • 96: Object name is a remote hardlink.
  • 97: Object name is a remote special file.
  • 98: Object name is a remote character device.
  • 99: Object name is a remote block device.
  • 100: Object name is a remote object.
  • 101: Object name is a remote object.
  • 102: Object name is a remote object.
  • 103: Object name is a remote object.
  • 104: Object name is a remote object.
  • 105: Object name is a remote object.
  • 106: Object name is a remote object.
  • 107: Object name is a remote object.
  • 108: Object name is a remote object.
  • 109: Object name is a remote object.
  • 110: Object name is a remote object.
  • 111: Object name is a remote object.
  • 112: Object name is a remote object.
  • 113: Object name is a remote object.
  • 114: Object name is a remote object.
  • 115: Object name is a remote object.
  • 116: Object name is a remote object.
  • 117: Object name is a remote object.
  • 118: Object name is a remote object.
  • 119: Object name is a remote object.
  • 120: Object name is a remote object.
  • 121: Object name is a remote object.
  • 122: Object name is a remote object.
  • 123: Object name is a remote object.
  • 124: Object name is a remote object.
  • 125: Object name is a remote object.
  • 126: Object name is a remote object.
  • 127: Object name is a remote object.
  • 128: Object name is a remote object.
  • 129: Object name is a remote object.
  • 130: Object name is a remote object.
  • 131: Object name is a remote object.
  • 132: Object name is a remote object.
  • 133: Object name is a remote object.
  • 134: Object name is a remote object.
  • 135: Object name is a remote object.
  • 136: Object name is a remote object.
  • 137: Object name is a remote object.
  • 138: Object name is a remote object.
  • 139: Object name is a remote object.
  • 140: Object name is a remote object.
  • 141: Object name is a remote object.
  • 142: Object name is a remote object.
  • 143: Object name is a remote object.
  • 144: Object name is a remote object.
  • 145: Object name is a remote object.
  • 146: Object name is a remote object.
  • 147: Object name is a remote object.
  • 148: Object name is a remote object.
  • 149: Object name is a remote object.
  • 150: Object name is a remote object.
  • 151: Object name is a remote object.
  • 152: Object name is a remote object.
  • 153: Object name is a remote object.
  • 154: Object name is a remote object.
  • 155: Object name is a remote object.
  • 156: Object name is a remote object.
  • 157: Object name is a remote object.
  • 158: Object name is a remote object.
  • 159: Object name is a remote object.
  • 160: Object name is a remote object.
  • 161: Object name is a remote object.
  • 162: Object name is a remote object.
  • 163: Object name is a remote object.
  • 164: Object name is a remote object.
  • 165: Object name is a remote object.
  • 166: Object name is a remote object.
  • 167: Object name is a remote object.
  • 168: Object name is a remote object.
  • 169: Object name is a remote object.
  • 170: Object name is a remote object.
  • 171: Object name is a remote object.
  • 172: Object name is a remote object.
  • 173: Object name is a remote object.
  • 174: Object name is a remote object.
  • 175: Object name is a remote object.
  • 176: Object name is a remote object.
  • 177: Object name is a remote object.
  • 178: Object name is a remote object.
  • 179: Object name is a remote object.
  • 180: Object name is a remote object.
  • 181: Object name is a remote object.
  • 182: Object name is a remote object.
  • 183: Object name is a remote object.
  • 184: Object name is a remote object.
  • 185: Object name is a remote object.
  • 186: Object name is a remote object.
  • 187: Object name is a remote object.
  • 188: Object name is a remote object.
  • 189: Object name is a remote object.
  • 190: Object name is a remote object.
  • 191: Object name is a remote object.
  • 192: Object name is a remote object.
  • 193: Object name is a remote object.
  • 194: Object name is a remote object.
  • 195: Object name is a remote object.
  • 196: Object name is a remote object.
  • 197: Object name is a remote object.
  • 198: Object name is a remote object.
  • 199: Object name is a remote object.
  • 200: Object name is a remote object.
  • 201: Object name is a remote object.
  • 202: Object name is a remote object.
  • 203: Object name is a remote object.
  • 204: Object name is a remote object.
  • 205: Object name is a remote object.
  • 206: Object name is a remote object.
  • 207: Object name is a remote object.
  • 208: Object name is a remote object.
  • 209: Object name is a remote object.
  • 210: Object name is a remote object.
  • 211: Object name is a remote object.
  • 212: Object name is a remote object.
  • 213: Object name is a remote object.
  • 214: Object name is a remote object.
  • 215: Object name is a remote object.
  • 216: Object name is a remote object.
  • 217: Object name is a remote object.
  • 218: Object name is a remote object.
  • 219: Object name is a remote object.
  • 220: Object name is a remote object.
  • 221: Object name is a remote object.
  • 222: Object name is a remote object.
  • 223: Object name is a remote object.
  • 224: Object name is a remote object.
  • 225: Object name is a remote object.
  • 226: Object name is a remote object.
  • 227: Object name is a remote object.
  • 228: Object name is a remote object.
  • 229: Object name is a remote object.
  • 230: Object name is a remote object.
  • 231: Object name is a remote object.
  • 232: Object name is a remote object.
  • 233: Object name is a remote object.
  • 234: Object name is a remote object.
  • 235: Object name is a remote object.
  • 236: Object name is a remote object.
  • 237: Object name is a remote object.
  • 238: Object name is a remote object.
  • 239: Object name is a remote object.
  • 240: Object name is a remote object.
  • 241: Object name is a remote object.
  • 242: Object name is a remote object.
  • 243: Object name is a remote object.
  • 244: Object name is a remote object.
  • 245: Object name is a remote object.
  • 246: Object name is a remote object.
  • 247: Object name is a remote object.
  • 248: Object name is a remote object.
  • 249: Object name is a remote object.
  • 250: Object name is a remote object.
  • 251: Object name is a remote object.
  • 252: Object name is a remote object.
  • 253: Object name is a remote object.
  • 254: Object name is a remote object.
  • 255: Unknown remote error.
  • Example: rsync -avz /local/dir/ user@remote:/remote/dir/ might return 23 if there are I/O errors on the destination.

Common Patterns

• Checking for success:

  command_to_run
  if [ $? -eq 0 ]; then
      echo "Command succeeded."
  else
      echo "Command failed with exit code $?."
  fi
  

  • Explanation: This checks the special shell variable $? which holds the exit code of the most recently executed foreground command.

• Ignoring errors:

  command_to_run || echo "Command failed, but I'm ignoring it."
  

  • Explanation: The || operator executes the command on the right only if the command on the left fails (returns a non-zero exit code).

• Executing a command only if the previous one fails:

  command_that_might_fail
  if [ $? -ne 0 ]; then
      echo "It failed! Running cleanup..."
      cleanup_command
  fi
  

  • Explanation: This pattern explicitly checks if the exit code is not zero (-ne) and then executes a recovery or cleanup action.

• Using set -e to exit on error:

  #!/bin/bash
  set -e
  echo "This will run."
  ls /nonexistent_directory # This will cause the script to exit immediately
  echo "This will NOT run."
  

  • Explanation: set -e (or set -o errexit) makes the script exit immediately if any command fails (returns a non-zero exit code). This is a common way to ensure scripts don’t continue after an error.

• Using set -o pipefail:

  #!/bin/bash
  set -e
  set -o pipefail
  
  # This pipeline will exit with code 1 (from grep) because of pipefail
  ls / | grep "nonexistent_pattern"
  echo "This line will not be reached."
  

  • Explanation: By default, if a pipeline has multiple commands, the exit code of the pipeline is the exit code of the last command. set -o pipefail makes the pipeline’s exit code the exit code of the first command in the pipeline that failed. Combined with set -e, this ensures scripts exit on any failure within a pipeline.

Gotchas

• Exit code 1 is not always a critical failure: Commands like grep often return 1 when a pattern is not found, which is expected behavior, not necessarily an error. Always consult the specific command’s documentation.
• Signals vs. Exit Codes: Exit codes in the 128 + n range indicate termination by a signal. For example, 137 means the process was killed by signal 9 (SIGKILL). This is different from a command returning a specific error code like 1 or 2.
• Subshells and $?: The $? variable only reflects the exit code of the most recently executed foreground command. If you run commands in subshells (e.g., within (...)) or background processes, $? might not behave as expected for those specific commands.
• set -e and || / &&: set -e can be overridden by explicit || or && constructs. A command that would normally cause set -e to exit might not if it’s part of an if condition or a logical OR/AND chain.

  set -e
  ls /nonexistent_directory || echo "Ignoring the error as requested." # Script continues
  

• Exit code 127 is common for PATH issues: If you get a "command not found" error (exit code 127), double-check your PATH environment variable and ensure the command is installed and accessible.