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FUD(8) Cyrus IMAP FUD(8)


fud - Cyrus IMAP documentation

Provide information about user mailboxes


fud [ -C config-file ] [ -U uses ] [ -T timeout ] [ -D ]


fud is a long lived datagram daemon started from master that provides information about when a user last read their mail, when mail last arrived in a user's mailbox, and how many messages are recent for that user.

fud reads its configuration options out of the imapd.conf(5) file unless specified otherwise by -C.

fud will automatically proxy any and all FUD requests to the appropriate backend server if it is running on a Cyrus Murder frontend machine.

To set up the FUD daemon, add this to your cyrus.conf:

fud cmd="fud" listen="fud" prefork=1 proto="udp"

and to /etc/services:

fud 4201/udp # Cyrus IMAP FUD Daemon


There is no specific FUD client. This shows how one might access FUD.

use Socket;
print( "Enter fud hostname: " );
$hostname = <>;
chomp( $hostname );
print( "Enter username to query: " );
$username = <>;
chomp( $username );
socket( FUD, PF_INET, SOCK_DGRAM, getprotobyname( "udp" ) )

or die( "failed to create udp socket: $!" ); $ipaddr = inet_aton( $hostname ); $portaddr = sockaddr_in( '4201', $ipaddr ); $fud_query = $username . '|user.' . $username; send( FUD, "$fud_query", 0, $portaddr ) == length( $fud_query )
or die( "failed to send fud query: $!" ); recv( FUD, $fud_response, 512, 0 )
or die( "recv() failed: $!" ); print( "FUD responded: $fud_response\n" ); exit( 0 );


Use the specified configuration file config-file rather than the default imapd.conf(5).

The maximum number of times that the process should be used for new connections before shutting down. The default is 250.

The number of seconds that the process will wait for a new connection before shutting down. Note that a value of 0 (zero) will disable the timeout. The default is 60.

Run external debugger specified in debug_command.


/etc/imapd.conf, /etc/cyrus.conf


Though not really a bug, fud will silently ignore any requests that it does not consider valid.

Also not really a bug, fud requires that the anonymous user has the 0 (zero) right on the mailbox in question. This is only a "bug" because 0 is not a standard IMAP ACL bit.

fud is an experimental interface meant to provide information to build a finger-like service around. Eventually it should be superseded by a more standards-based protocol.


imapd.conf(5), cyrus.conf(5)


The Cyrus Team, Nic Bernstein (Onlight)


1993–2024, The Cyrus Team

May 6, 2024 3.8.3