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Linux in a Nutshell

This directory of Linux commands is from Linux in a Nutshell, 5th Edition.

Click on any of the 687 commands below to get a description and list of available options. All links in the command summaries point to the online version of the book on Safari Bookshelf.

Buy it now, or read it online on Safari Bookshelf.


ssh-add [options] [files] ssh-add -e|-s reader

Add RSA or DSA identities to the authentication agent (see ssh-agent), which must be running and must be an ancestor of the current process. ssh-add reads the files created by ssh-keygen for private keys. It reads the information in these private keys to obtain RSA or DSA identities. With no arguments specified, ssh-add adds the files $HOME/.ssh/id_rsa, $HOME/.ssh/id_dsa, and $HOME/.ssh/identity. If any files are specified, it adds those instead, prompting for a passphrase if required.



Confirm identities being added, by running the program specified in the SSH_ASKPASS environment variable (see the ssh command). A 0 exit status from the program indicates successful confirmation.


Remove an identity from the agent instead of adding one.


Delete all identities from the agent.

-e reader

Remove key in specified smartcard reader.


List fingerprints of all identities known to the agent.


List public key parameters of all identities known to the agent.

-s reader

Add key in smartcard reader.

-t life

Set maximum lifetime when adding identities to an agent. The value of life can be in seconds or another time format specified in sshd.


Lock the agent with a password.


Unlock the agent.

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