Linux su vs sudo vs sudo su vs sudo -i: Key Differences Explained

sudo vs su: Core Differences

Password requirement: sudo prompts for the current user's password, while su requires the target user's password (typically root).

Scope of privilege elevation: sudo runs a single command with elevated privileges and then returns to the original shell. su starts a new interactive shell as the target user, allowing multiple commands until the user explicitly exits.

Reference: Linux 命令 su 和 sudo 的区别 (http://mp.weixin.qq.com/s?__biz=MzAwMjg1NjY3Nw==&mid=2247518621&idx=2&sn=dec71be1e4b7dbf88911bdf042b66434&chksm=9ac6ca17adb14301b8ea02d69d0dd61c90ede6733c8e1b7463191ff42c23273bf6c60c00b45b&scene=21#wechat_redirect)

Switching User Identity with su

By default, su only changes the user identity; environment variables remain those of the original user.

Using su - (or su - username) switches both identity and environment variables to the target user's environment. The hyphen cannot be omitted if the new environment is required for certain operations.

Examples: su root — after entering the root password, the current working directory stays unchanged. su - root — after entering the root password, the working directory changes to /root.

sudo Command Variants and Behavior

The following forms are functionally equivalent: sudo -i root, sudo - root, sudo -i, sudo -, sudo root. All prompt for the current user's password and require the user to be listed in /etc/sudoers.

sudo vs su summary: sudo: Temporarily elevates to superuser (usually root) for a single command. Uses the current user's password. Ubuntu defaults to a 15‑minute timeout before re‑prompting. su: Switches to the specified user (defaults to root). Uses the target user's password. No automatic timeout; the session persists until exit or logout.

sudo -i starts an interactive root shell without repeated password prompts. The prompt changes from $ to #. Exit with exit or logout. The invoking user must be in sudoers.