best counter
close
close
sshd re-exec requires execution with an absolute path

sshd re-exec requires execution with an absolute path

3 min read 19-12-2024
sshd re-exec requires execution with an absolute path

The error message "sshd_config: re-exec requires execution with an absolute path" is a common issue encountered when configuring the SSH daemon (sshd). This article will delve into the root cause of this error, provide step-by-step solutions, and offer best practices for preventing it in the future. Understanding this error is crucial for maintaining secure and functional SSH access.

Understanding the Error

The error "sshd_config: re-exec requires execution with an absolute path" arises when the ExecStart or ExecStop directives within your SSH daemon configuration file (sshd_config) specify a command path that is relative rather than absolute. SSHD, for security reasons, strictly requires absolute paths for commands it executes. A relative path leaves the command open to potential manipulation and security vulnerabilities. Think of it as SSH saying, "I need the exact location of this program, not just a vague hint."

Locating Your SSH Configuration File

Before troubleshooting, it's vital to locate your sshd_config file. The location varies depending on your operating system:

  • Debian/Ubuntu/Linux Mint: /etc/ssh/sshd_config
  • Red Hat/CentOS/Fedora: /etc/ssh/sshd_config
  • macOS: /etc/sshd_config

Troubleshooting the Error: Step-by-Step Guide

The solution is straightforward: replace any relative paths in your sshd_config file with absolute paths. Here's a step-by-step guide:

  1. Open the sshd_config file: Use a text editor with root or sudo privileges. For example, on most systems: sudo nano /etc/ssh/sshd_config

  2. Identify the offending lines: Search for lines containing ExecStart, ExecStop, or similar directives that might be using relative paths. These lines typically specify commands the SSH daemon executes. A relative path might look like ExecStart=/usr/local/bin/mycommand.

  3. Replace relative paths with absolute paths: Find the absolute path of the executable. You can use the which command in your terminal. For example, to find the absolute path of mycommand, run which mycommand. This will output the full path, something like /usr/local/bin/mycommand. Replace the relative path in your sshd_config file with this absolute path.

  4. Save the changes: Save the modified sshd_config file.

  5. Restart the SSH daemon: This is crucial to apply your changes. The command varies slightly by distribution:

    • Systemd (most modern Linux distributions): sudo systemctl restart sshd
    • SysVinit (older Linux distributions): sudo /etc/init.d/sshd restart
    • macOS: sudo launchctl unload -w /System/Library/LaunchDaemons/org.ssh.sshd.plist; sudo launchctl load -w /System/Library/LaunchDaemons/org.ssh.sshd.plist
  6. Verify the fix: Attempt to connect to your server via SSH. If the error is resolved, you should be able to connect without any issues.

Example Scenario and Fix

Let's say your sshd_config file contains the following line:

ExecStart=/usr/local/bin/mycustomscript

If this mycustomscript is located at /usr/local/bin/mycustomscript, this line is already correct. However, if /usr/local/bin was not added to your PATH, it should be replaced with the absolute path. If it's actually in /home/user/scripts/mycustomscript, you'd change the line to:

ExecStart=/home/user/scripts/mycustomscript

Remember to restart SSHD after making any changes to the sshd_config file.

Best Practices and Prevention

To avoid this error in the future, always use absolute paths when specifying commands within the sshd_config file. This simple practice greatly enhances the security and reliability of your SSH server. Always double-check your paths before saving your changes and restarting the SSH daemon.

By following these steps and best practices, you can effectively resolve the "sshd_config: re-exec requires execution with an absolute path" error and ensure the smooth and secure operation of your SSH server. Remember to always prioritize security in your server configuration.

Related Posts