how do i know the current shell is logged in from ssh

You can determine if your current shell session was established via SSH by checking specific environment variables or using system commands.

1. Environment Variables:

When you connect via SSH, several environment variables are typically set. You can check for their presence:

• SSH\_CLIENT: Contains the client IP address, client port, and server port.
• SSH\_CONNECTION: Contains the client IP address, client port, server IP address, and server port.
• SSH\_TTY: Contains the name of the pseudo-terminal allocated for the SSH session.

You can check these using the echo command:

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echo $SSH_CLIENT
echo $SSH_CONNECTION
echo $SSH_TTY

If these variables are populated with values, it indicates an SSH session. If they are empty, it's likely a local console session.

2. who or w Command:

The who and w commands display information about users currently logged into the system.

• who:

  Shows your username, terminal, and login time. If the FROM column shows an IP address or hostname, it indicates a remote connection.
• w:

  Provides similar information to who but also includes details about current processes and activity.

To see information specific to your current session, you can use:

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who am i

or

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who -m

The output will show your username, the terminal you're using (e.g., pts/0), and the remote host or IP address if connected via SSH.

3. loginctl (for systems using systemd):

If your system uses systemd, you can use loginctl to query session information.

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loginctl show-session --value -p Remote "$XDG_SESSION_ID"

If the output is yes, it indicates a remote session, typically through SSH.

4. ps Command and pstree:

You can also examine the process tree to see if sshd is an ancestor of your current shell.

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pstree -s -p $$ | grep -c '\-sshd('

If the output is 1, it means sshd is in the process ancestry, indicating an SSH session.

In summary: Checking for the presence of SSH_CLIENT, SSH_CONNECTION, or SSH_TTY environment variables is often the most direct way to determine if your current shell is logged in from SSH. Alternatively, using who am i or pstree can also provide this information.