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# Linux su Command [ Linux Command Manual](#) The Linux su (short for switch user) command is used to switch user identity. Except for root, you need to enter the user's password. Usage permissions: All users. ### Syntax su For example: su # Switch to root, keep current environment su - # Switch to root, load root's full environment su root # Explicitly specify switching to root user Switch to other users: su username su - username su -l username **Parameter Description**: * `-` or `-l` or `--login`: Provides an environment similar to a direct login * `-c command`: Executes the specified command and then exits * `-s shell`: Specifies the shell to use * `-p` or `--preserve-environment`: Preserves current environment variables ### Examples Temporarily execute commands as root: su -c "apt update && apt upgrade" root Switch to a service user for debugging: su - www-data su -s /bin/bash www-data # If the default shell is /bin/false Use in scripts: su - postgres -c "psql -c 'SELECT version();'" Exit su session: exit # Exit current su sessionCtrl+D # Also can exit * * * ## Difference between su and su - **`su` (non-login switch):** * Keeps current user's environment variables * Working directory remains unchanged * PATH and other environment variables remain unchanged **`su -` (login switch):** * Loads the target user's full environment * Switches to the target user's home directory * Resets PATH, HOME, and other environment variables * Executes the target user's login scripts ### Example Comparison # Current user: john, working directory: /home/john pwd # /home/john echo $HOME # /home/john su root pwd # /home/john (directory unchanged) echo $HOME # /home/john (environment unchanged)exit su - root pwd # /root (switched to root's home directory) echo $HOME # /root (full environment)exit * * * ## Difference between su vs sudo | Feature | su | sudo | | --- | --- | --- | | Requires Password | Target user's password | Current user's password | | Session Duration | Until manual exit | Single command or short-time cache | | Configuration Complexity | Simple | Requires sudoers configuration | | Security | Requires knowing root password | More granular permission control | | Audit | Limited | More detailed logs | Although the su command is simple and direct, in modern system administration, sudo is usually the more recommended choice because it provides better security and auditing capabilities. * * * ## Security Precautions * Avoid sharing the root password * Use `su -` to ensure a complete environment switch * Exit su sessions promptly * Prefer using sudo in production environments * Monitor su usage logs (usually in /var/log/auth.log) [ Linux Command Manual](#)