NAME¶

rpc.gssd - rpcsec_gss daemon

SYNOPSIS¶

rpc.gssd [-f] [-n] [-k keytab] [-l] [-p pipefsdir] [-v] [-r] [-d ccachedir]

DESCRIPTION¶

The rpcsec_gss protocol gives a means of using the gss-api generic security api to provide security for protocols using rpc (in particular, nfs). Before exchanging any rpc requests using rpcsec_gss, the rpc client must first establish a security context. The linux kernel's implementation of rpcsec_gss depends on the userspace daemon rpc.gssd to establish security contexts. The rpc.gssd daemon uses files in the rpc_pipefs filesystem to communicate with the kernel.

OPTIONS¶

-f

Runs rpc.gssd in the foreground and sends output to stderr (as opposed to syslogd)

-n

By default, rpc.gssd treats accesses by the user with UID 0 specially, and uses "machine credentials" for all accesses by that user which require Kerberos authentication. With the -n option, "machine credentials" will not be used for accesses by UID 0. Instead, credentials must be obtained manually like all other users. Use of this option means that "root" must manually obtain Kerberos credentials before attempting to mount an nfs filesystem requiring Kerberos authentication.

-k keytab

Tells rpc.gssd to use the keys found in keytab to obtain "machine credentials". The default value is "/etc/krb5.keytab".

Previous versions of rpc.gssd used only "nfs/*" keys found within the keytab. To be more consistent with other implementations, we now look for specific keytab entries. The search order for keytabs to be used for "machine credentials" is now:
<HOSTNAME>$@<REALM>
root/<hostname>@<REALM>
nfs/<hostname>@<REALM>
host/<hostname>@<REALM>
root/<anyname>@<REALM>
nfs/<anyname>@<REALM>
host/<anyname>@<REALM>

If this search order does not use the correct key then provide a keytab file that contains only correct keys.

-l

Tells rpc.gssd to limit session keys to Single DES even if the kernel supports stronger encryption types. Service ticket encryption is still governed by what the KDC believes the target server supports. This way the client can access a server that has strong keys in its keytab for ticket decryption but whose kernel only supports Single DES.

The alternative is to put only Single DES keys in the server's keytab and limit encryption types for its principal to Single DES on the KDC which will cause service tickets for this server to be encrypted using only Single DES and (as a side-effect) contain only Single DES session keys.

This legacy behaviour is only required for older servers (pre nfs-utils-1.2.4). If the server has a recent kernel, Kerberos implementation and nfs-utils it will work just fine with stronger encryption.

Note: This option is only available with Kerberos libraries that support setable encryption types.

-p path

Tells rpc.gssd where to look for the rpc_pipefs filesystem. The default value is "/var/lib/nfs/rpc_pipefs".

-d directory

Tells rpc.gssd where to look for Kerberos credential files. The default value is "/tmp". This can also be a colon separated list of directories to be searched for Kerberos credential files. Note that if machine credentials are being stored in files, then the first directory on this list is where the machine credentials are stored.

-v

Increases the verbosity of the output (can be specified multiple times).

-r

If the rpcsec_gss library supports setting debug level, increases the verbosity of the output (can be specified multiple times).

-R realm

Kerberos tickets from this realm will be preferred when scanning available credentials cache files to be used to create a context. By default, the default realm, as configured in the Kerberos configuration file, is preferred.

-t timeout

Timeout, in seconds, for kernel gss contexts. This option allows you to force new kernel contexts to be negotiated after timeout seconds, which allows changing Kerberos tickets and identities frequently. The default is no explicit timeout, which means the kernel context will live the lifetime of the Kerberos service ticket used in its creation.

-T timeout

Timeout, in seconds, to create an RPC connection with a server while establishing an authenticated gss context for a user. The default timeout is set to 5 seconds. If you get messages like "WARNING: can't create tcp rpc_clnt to server %servername% for user with uid %uid%: RPC: Remote system error - Connection timed out", you should consider an increase of this timeout.

SEE ALSO¶

rpc.svcgssd(8)

AUTHORS¶

Dug Song <dugsong@umich.edu>
Andy Adamson <andros@umich.edu>
Marius Aamodt Eriksen <marius@umich.edu>
J. Bruce Fields <bfields@umich.edu>