ssh-user: How to Specify SSH User

Overview

`ssh-user` refers to the user account used for authentication when connecting to a remote system via the `ssh` protocol. This is a core part of the `ssh` command, allowing you to perform remote operations with the privileges of a specific user.

Importance of Specifying User

Authentication: Specifies which account to log in with when connecting to the remote server.
Permission Management: Each user has specific permissions, so you connect with the appropriate user to perform necessary tasks.
Security: It is recommended for security to avoid direct connection with the root account and use a regular user account instead.

Usage Examples

Since `ssh-user` itself is not a command, this section demonstrates various ways to specify a user through the `ssh` command.

Basic User Specification

ssh myuser@example.com

In the most common format, the user to connect as is specified in the `[username]@[hostname]` format.

Using the -l Option

ssh -l myuser example.com

You can also specify the username separately using the `-l` option. This works identically to the `user@host` format.

Utilizing the ~/.ssh/config File

You can simplify user specification by saving host-specific settings in the `~/.ssh/config` file. This method is very useful when connecting to multiple servers, as it allows you to predefine various settings such as username, port, and authentication keys.

Example ~/.ssh/config Content

The following is an example of setting up the `myuser` account with the alias `myserver` in the `~/.ssh/config` file. You need to add this content to your actual file. Host myserver HostName example.com User myuser Port 22 IdentityFile ~/.ssh/id_rsa

Connecting with Config Settings

ssh myserver

After applying the `~/.ssh/config` settings above, connect as the `myuser` account using the alias `myserver`.

Tips & Precautions

Useful tips and security precautions when specifying SSH users.

Default Username

If the username on your local system is the same as the username on the remote system, you can omit the username and connect using `ssh example.com`. In this case, the SSH client will attempt to connect using your current local username.

Same Username: ssh example.com
Different Username: ssh myuser@example.com

Restricting Root Login

For security reasons, it is not recommended to SSH directly as the `root` account. Instead, it is advisable to connect as a regular user and then use the `sudo` command to perform administrative tasks. You can disable direct `root` login by setting `PermitRootLogin no` in the `/etc/ssh/sshd_config` file on the remote server.

Managing Per-User Authentication Keys

Each user account can have its own SSH key pair, which is stored in files like `~/.ssh/id_rsa` (private key) and `~/.ssh/id_rsa.pub` (public key). By registering your public key in the `~/.ssh/authorized_keys` file on the remote server, you can connect without a password.