4 .\" Copyright (C) 2003 J. Bruce Fields <bfields@umich.edu>
6 .TH rpc.gssd 8 "20 Feb 2013"
8 rpc.gssd \- RPCSEC_GSS daemon
23 The RPCSEC_GSS protocol, defined in RFC 5403, is used to provide
24 strong security for RPC-based protocols such as NFS.
26 Before exchanging RPC requests using RPCSEC_GSS, an RPC client must
28 .IR "security context" .
29 A security context is shared state on each
30 end of a network transport that enables GSS-API security services.
32 Security contexts are established using
33 .IR "security credentials" .
34 A credential grants temporary access to a secure network service,
35 much as a railway ticket grants temporary access to use a rail service.
37 A user typically obtains a credential by providing a password to the
39 command, or via a PAM library at login time.
40 A credential acquired with a
46 for more on principals).
48 For certain operations, a credential is required
49 which represents no user,
50 is otherwise unprivileged,
51 and is always available.
52 This is referred to as a
53 .IR "machine credential" .
55 Machine credentials are typically established using a
56 .IR "service principal" ,
57 whose encrypted password, called its
59 is stored in a file, called a
61 to avoid requiring a user prompt.
62 A machine credential effectively does not expire because the system
63 can renew it as needed without user intervention.
65 Once obtained, credentials are typically stored in local temporary files
66 with well-known pathnames.
68 To establish GSS security contexts using these credential files,
69 the Linux kernel RPC client depends on a userspace daemon called
73 daemon uses the rpc_pipefs filesystem to communicate with the kernel.
75 When a user authenticates using a command such as
77 the resulting credential is stored in a file with a well-known name
78 constructed using the user's UID.
80 To interact with an NFS server
81 on behalf of a particular Kerberos-authenticated user,
82 the Linux kernel RPC client requests that
84 initialize a security context with the credential
85 in that user's credential file.
87 Typically, credential files are placed in
91 can search for credential files in more than one directory.
92 See the description of the
95 .SS Machine Credentials
96 A user credential is established by a user and
97 is then shared with the kernel and
99 A machine credential is established by
101 for the kernel when there is no user.
104 must already have the materials on hand to establish this credential
105 without requiring user intervention.
108 searches the local system's keytab for a principal and key to use
109 to establish the machine credential.
114 contains principals and keys that can be used to obtain machine credentials.
117 searches in the following order for a principal to use.
118 The first matching credential is used.
119 For the search, <hostname> and <REALM> are replaced with the local
120 system's hostname and Kerberos realm.
124 root/<hostname>@<REALM>
126 nfs/<hostname>@<REALM>
128 host/<hostname>@<REALM>
130 root/<anyname>@<REALM>
132 nfs/<anyname>@<REALM>
134 host/<anyname>@<REALM>
136 The <anyname> entries match on the service name and realm, but ignore the hostname.
137 These can be used if a principal matching the local host's name is not found.
139 Note that the first principal in the search order is a user principal
140 that enables Kerberized NFS when the local system is joined
141 to an Active Directory domain using Samba.
142 A password for this principal must be provided in the local system's keytab.
144 You can specify another keytab by using the
148 does not exist or does not provide one of these principals.
149 .SS Credentials for UID 0
150 UID 0 is a special case.
153 uses the system's machine credentials for UID 0 accesses
154 that require GSS authentication.
155 This limits the privileges of the root user
156 when accessing network resources that require authentication.
162 if you'd like to force the root user to obtain a user credential
163 rather than use the local system's machine credential.
168 the kernel continues to request a GSS context established
169 with a machine credential for NFSv4 operations,
170 such as SETCLIENTID or RENEW, that manage state.
173 cannot obtain a machine credential (say, the local system has
174 no keytab), NFSv4 operations that require machine credentials will fail.
180 in the foreground and sends output to stderr (as opposed to syslogd)
183 When specified, UID 0 is forced to obtain user credentials
184 which are used instead of the local system's machine credentials.
189 to use the keys found in
191 to obtain machine credentials.
193 .IR /etc/krb5.keytab .
198 to limit session keys to Single DES even if the kernel supports stronger
199 encryption types. Service ticket encryption is still governed by what
200 the KDC believes the target server supports. This way the client can
201 access a server that has strong keys in its keytab for ticket decryption
202 but whose kernel only supports Single DES.
204 The alternative is to put only Single DES keys in the server's keytab
205 and limit encryption types for its principal to Single DES on the KDC
206 which will cause service tickets for this server to be encrypted using
207 only Single DES and (as a side-effect) contain only Single DES session
210 This legacy behaviour is only required for older servers
211 (pre nfs-utils-1.2.4). If the server has a recent kernel, Kerberos
212 implementation and nfs-utils it will work just fine with stronger
216 This option is only available with Kerberos libraries that
217 support setable encryption types.
222 where to look for the rpc_pipefs filesystem. The default value is
223 .IR /var/lib/nfs/rpc_pipefs .
225 .BI "-d " search-path
226 This option specifies a colon separated list of directories that
228 searches for credential files. The default value is
229 .IR /tmp:/run/user/%U .
230 The literal sequence "%U" can be specified to substitue the UID
231 of the user for whom credentials are being searched.
234 By default, machine credentials are stored in files in the first
235 directory in the credential directory search path (see the
241 stores machine credentials in memory instead.
244 Increases the verbosity of the output (can be specified multiple times).
247 If the RPCSEC_GSS library supports setting debug level,
248 increases the verbosity of the output (can be specified multiple times).
251 Kerberos tickets from this
253 will be preferred when scanning available credentials cache files to be
254 used to create a context. By default, the default realm, as configured
255 in the Kerberos configuration file, is preferred.
258 Timeout, in seconds, for kernel GSS contexts. This option allows you to force
259 new kernel contexts to be negotiated after
261 seconds, which allows changing Kerberos tickets and identities frequently.
262 The default is no explicit timeout, which means the kernel context will live
263 the lifetime of the Kerberos service ticket used in its creation.
271 Dug Song <dugsong@umich.edu>
273 Andy Adamson <andros@umich.edu>
275 Marius Aamodt Eriksen <marius@umich.edu>
277 J. Bruce Fields <bfields@umich.edu>