ident

Display RCS identification strings in a file

$ ident [path/to/file]

$ ident -q [path/to/file1 path/to/file2 ...]

$ cat [path/to/file] | ident

ident [-46aAdghV] [-p port] [-t timeout] [-w wait] host [service]

-4, --ipv4
    Force IPv4 protocol

-6, --ipv6
    Force IPv6 protocol

-a, --address
    Display numeric address instead of hostname

-A, --address-resolve
    Resolve numeric address to hostname

-d, --debug
    Enable debug output

-g, --no-portmap
    Do not map port numbers to service names

-h, --help
    Display help and exit

-p, --local-port=PORT
    Use specified local port

-t, --timeout=NUM
    Set timeout in seconds (default 30)

-V, --version
    Show version information

-w, --wait=NUM
    Maximum wait time in seconds (default 120)

ident is a command-line utility that implements the client side of the Identification Protocol, as defined in RFC 1413. This protocol, originally known as the Auth server protocol, allows a client to query a remote host's identd daemon for information about the owner of a specific TCP/IP connection.

To use it, specify a remote host and optionally a service or port. ident connects to port 113 on the remote host and sends a query in the format local-port, remote-port. The remote identd responds with details such as the user ID, system name, and sometimes additional info like the user's full name or idle time.

Commonly used in the past for logging incoming connections in services like IRC, mail servers, or FTP to identify users. For example, when connecting from your local port 12345 to remotehost:25, ident queries remotehost's identd about that connection.

However, due to privacy concerns and security risks (e.g., information leakage, DoS potential), identd is rarely deployed today. Responses may be unreliable or unavailable on modern systems. The tool supports both IPv4 and IPv6, with configurable timeouts and debugging.

Ident protocol is obsolete and insecure; many hosts do not run identd, leading to timeouts or errors. Avoid relying on it for authentication.

ident example.com 80
Queries identd on example.com for connection to port 80.

Typical response: 12345, 80 : USERID : UNIX : kzak (localport,remoteport : userid : os : username)

Part of the util-linux package since early 2000s, maintained by Red Hat and community. Implements RFC 1413 (1993) for legacy network identification.

nc(1), telnet(1), host(1), finger(1)