nfs-utils/SOURCES/nfs-utils-1.3.0/utils/gssd/gssd.man - actifio - Git at Google

 .\"
 .\" rpc.gssd(8)
 .\"
 .\" Copyright (C) 2003 J. Bruce Fields <bfields@umich.edu>
 .\"
 .TH rpc.gssd 8 "20 Feb 2013"
 .SH NAME
 rpc.gssd \- RPCSEC_GSS daemon
 .SH SYNOPSIS
 .B rpc.gssd
 .RB [ \-DfMnlvr ]
 .RB [ \-k
 .IR keytab ]
 .RB [ \-p
 .IR pipefsdir ]
 .RB [ \-d
 .IR ccachedir ]
 .RB [ \-t
 .IR timeout ]
 .RB [ \-R
 .IR realm ]
 .SH INTRODUCTION
 The RPCSEC_GSS protocol, defined in RFC 5403, is used to provide
 strong security for RPC-based protocols such as NFS.
 .P
 Before exchanging RPC requests using RPCSEC_GSS, an RPC client must
 establish a GSS
 .IR "security context" .
 A security context is shared state on each
 end of a network transport that enables GSS-API security services.
 .P
 Security contexts are established using
 .IR "security credentials" .
 A credential grants temporary access to a secure network service,
 much as a railway ticket grants temporary access to use a rail service.
 .P
 A user typically obtains a credential by providing a password to the
 .BR kinit (1)
 command, or via a PAM library at login time.
 A credential acquired with a
 .I user principal
 is known as a
 .I user credential
 (see
 .BR kerberos (1)
 for more on principals).
 .P
 For certain operations, a credential is required
 which represents no user,
 is otherwise unprivileged,
 and is always available.
 This is referred to as a
 .IR "machine credential" .
 .P
 Machine credentials are typically established using a
 .IR "service principal" ,
 whose encrypted password, called its
 .IR key ,
 is stored in a file, called a
 .IR keytab ,
 to avoid requiring a user prompt.
 A machine credential effectively does not expire because the system
 can renew it as needed without user intervention.
 .P
 Once obtained, credentials are typically stored in local temporary files
 with well-known pathnames.
 .SH DESCRIPTION
 To establish GSS security contexts using these credential files,
 the Linux kernel RPC client depends on a userspace daemon called
 .BR rpc.gssd .
 The
 .B rpc.gssd
 daemon uses the rpc_pipefs filesystem to communicate with the kernel.
 .SS User Credentials
 When a user authenticates using a command such as
 .BR kinit (1),
 the resulting credential is stored in a file with a well-known name
 constructed using the user's UID.
 .P
 To interact with an NFS server
 on behalf of a particular Kerberos-authenticated user,
 the Linux kernel RPC client requests that
 .B rpc.gssd
 initialize a security context with the credential
 in that user's credential file.
 .P
 Typically, credential files are placed in
 .IR /tmp .
 However,
 .B rpc.gssd
 can search for credential files in more than one directory.
 See the description of the
 .B -d
 option for details.
 .SS Machine Credentials
 A user credential is established by a user and
 is then shared with the kernel and
 .BR rpc.gssd .
 A machine credential is established by
 .B rpc.gssd
 for the kernel when there is no user.
 Therefore
 .B rpc.gssd
 must already have the materials on hand to establish this credential
 without requiring user intervention.
 .P
 .B rpc.gssd
 searches the local system's keytab for a principal and key to use
 to establish the machine credential.
 By default,
 .B rpc.gssd
 assumes the file
 .I /etc/krb5.keytab
 contains principals and keys that can be used to obtain machine credentials.
 .P
 .B rpc.gssd
 searches in the following order for a principal to use.
 The first matching credential is used.
 For the search, <hostname> and <REALM> are replaced with the local
 system's hostname and Kerberos realm.
 .sp
    <HOSTNAME>$@<REALM>
 .br
    root/<hostname>@<REALM>
 .br
    nfs/<hostname>@<REALM>
 .br
    host/<hostname>@<REALM>
 .br
    root/<anyname>@<REALM>
 .br
    nfs/<anyname>@<REALM>
 .br
    host/<anyname>@<REALM>
 .sp
 The <anyname> entries match on the service name and realm, but ignore the hostname.
 These can be used if a principal matching the local host's name is not found.
 .P
 Note that the first principal in the search order is a user principal
 that enables Kerberized NFS when the local system is joined
 to an Active Directory domain using Samba.
 A password for this principal must be provided in the local system's keytab.
 .P
 You can specify another keytab by using the
 .B -k
 option if
 .I /etc/krb5.keytab
 does not exist or does not provide one of these principals.
 .SS Credentials for UID 0
 UID 0 is a special case.
 By default
 .B rpc.gssd
 uses the system's machine credentials for UID 0 accesses
 that require GSS authentication.
 This limits the privileges of the root user
 when accessing network resources that require authentication.
 .P
 Specify the
 .B -n
 option when starting
 .B rpc.gssd
 if you'd like to force the root user to obtain a user credential
 rather than use the local system's machine credential.
 .P
 When
 .B -n
 is specified,
 the kernel continues to request a GSS context established
 with a machine credential for NFSv4 operations,
 such as SETCLIENTID or RENEW, that manage state.
 If
 .B rpc.gssd
 cannot obtain a machine credential (say, the local system has
 no keytab), NFSv4 operations that require machine credentials will fail.
 .SS Encryption types
 A realm administrator can choose to add keys encoded in a number of different
 encryption types to the local system's keytab.
 For instance, a host/ principal might have keys for the
 .BR aes256-cts-hmac-sha1-96 ,
 .BR aes128-cts-hmac-sha1-96 ,
 .BR des3-cbc-sha1 ", and"
 .BR arcfour-hmac " encryption types."
 This permits
 .B rpc.gssd
 to choose an appropriate encryption type that the target NFS server
 supports.
 .P
 These encryption types are stronger than legacy single-DES encryption types.
 To interoperate in environments where servers support
 only weak encryption types,
 you can restrict your client to use only single-DES encryption types
 by specifying the
 .B -l
 option when starting
 .BR rpc.gssd .
 .SH OPTIONS
 .TP
 .B \-D
 The server name passed to GSSAPI for authentication is normally the
 name exactly as requested.  e.g. for NFS
 it is the server name in the "servername:/path" mount request.  Only if this
 servername appears to be an IP address (IPv4 or IPv6) or an
 unqualified name (no dots) will a reverse DNS lookup
 will be performed to get the canoncial server name.

 If
 .B \-D
 is present, a reverse DNS lookup will
 .I always
 be used, even if the server name looks like a canonical name.  So it
 is needed if partially qualified, or non canonical names are regularly
 used.

 Using
 .B \-D
 can introduce a security vulnerability, so it is recommended that
 .B \-D
 not be used, and that canonical names always be used when requesting
 services.
 .TP
 .B -f
 Runs
 .B rpc.gssd
 in the foreground and sends output to stderr (as opposed to syslogd)
 .TP
 .B -n
 When specified, UID 0 is forced to obtain user credentials
 which are used instead of the local system's machine credentials.
 .TP
 .BI "-k " keytab
 Tells
 .B rpc.gssd
 to use the keys found in
 .I keytab
 to obtain machine credentials.
 The default value is
 .IR /etc/krb5.keytab .
 .TP
 .B -l
 When specified, restricts
 .B rpc.gssd
 to sessions to weak encryption types such as
 .BR des-cbc-crc .
 This option is available only when the local system's Kerberos library
 supports settable encryption types.
 .TP
 .BI "-p " path
 Tells
 .B rpc.gssd
 where to look for the rpc_pipefs filesystem.  The default value is
 .IR /var/lib/nfs/rpc_pipefs .
 .TP
 .BI "-d " search-path
 This option specifies a colon separated list of directories that
 .B rpc.gssd
 searches for credential files.  The default value is
 .IR /tmp:/run/user/%U .
 The literal sequence "%U" can be specified to substitue the UID
 of the user for whom credentials are being searched.
 .TP
 .B -M
 By default, machine credentials are stored in files in the first
 directory in the credential directory search path (see the
 .B -d
 option).  When
 .B -M
 is set,
 .B rpc.gssd
 stores machine credentials in memory instead.
 .TP
 .B -v
 Increases the verbosity of the output (can be specified multiple times).
 .TP
 .B -r
 If the RPCSEC_GSS library supports setting debug level,
 increases the verbosity of the output (can be specified multiple times).
 .TP
 .BI "-R " realm
 Kerberos tickets from this
 .I 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.
 .TP
 .BI "-t " timeout
 Timeout, in seconds, for kernel GSS contexts. This option allows you to force
 new kernel contexts to be negotiated after
 .I 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.
 .SH SEE ALSO
 .BR rpc.svcgssd (8),
 .BR kerberos (1),
 .BR kinit (1),
 .BR krb5.conf (5)
 .SH AUTHORS
 .br
 Dug Song <dugsong@umich.edu>
 .br
 Andy Adamson <andros@umich.edu>
 .br
 Marius Aamodt Eriksen <marius@umich.edu>
 .br
 J. Bruce Fields <bfields@umich.edu>
	.\"
	.\" rpc.gssd(8)
	.\"
	.\" Copyright (C) 2003 J. Bruce Fields <bfields@umich.edu>
	.\"
	.TH rpc.gssd 8 "20 Feb 2013"
	.SH NAME
	rpc.gssd \- RPCSEC_GSS daemon
	.SH SYNOPSIS
	.B rpc.gssd
	.RB [ \-DfMnlvr ]
	.RB [ \-k
	.IR keytab ]
	.RB [ \-p
	.IR pipefsdir ]
	.RB [ \-d
	.IR ccachedir ]
	.RB [ \-t
	.IR timeout ]
	.RB [ \-R
	.IR realm ]
	.SH INTRODUCTION
	The RPCSEC_GSS protocol, defined in RFC 5403, is used to provide
	strong security for RPC-based protocols such as NFS.
	.P
	Before exchanging RPC requests using RPCSEC_GSS, an RPC client must
	establish a GSS
	.IR "security context" .
	A security context is shared state on each
	end of a network transport that enables GSS-API security services.
	.P
	Security contexts are established using
	.IR "security credentials" .
	A credential grants temporary access to a secure network service,
	much as a railway ticket grants temporary access to use a rail service.
	.P
	A user typically obtains a credential by providing a password to the
	.BR kinit (1)
	command, or via a PAM library at login time.
	A credential acquired with a
	.I user principal
	is known as a
	.I user credential
	(see
	.BR kerberos (1)
	for more on principals).
	.P
	For certain operations, a credential is required
	which represents no user,
	is otherwise unprivileged,
	and is always available.
	This is referred to as a
	.IR "machine credential" .
	.P
	Machine credentials are typically established using a
	.IR "service principal" ,
	whose encrypted password, called its
	.IR key ,
	is stored in a file, called a
	.IR keytab ,
	to avoid requiring a user prompt.
	A machine credential effectively does not expire because the system
	can renew it as needed without user intervention.
	.P
	Once obtained, credentials are typically stored in local temporary files
	with well-known pathnames.
	.SH DESCRIPTION
	To establish GSS security contexts using these credential files,
	the Linux kernel RPC client depends on a userspace daemon called
	.BR rpc.gssd .
	The
	.B rpc.gssd
	daemon uses the rpc_pipefs filesystem to communicate with the kernel.
	.SS User Credentials
	When a user authenticates using a command such as
	.BR kinit (1),
	the resulting credential is stored in a file with a well-known name
	constructed using the user's UID.
	.P
	To interact with an NFS server
	on behalf of a particular Kerberos-authenticated user,
	the Linux kernel RPC client requests that
	.B rpc.gssd
	initialize a security context with the credential
	in that user's credential file.
	.P
	Typically, credential files are placed in
	.IR /tmp .
	However,
	.B rpc.gssd
	can search for credential files in more than one directory.
	See the description of the
	.B -d
	option for details.
	.SS Machine Credentials
	A user credential is established by a user and
	is then shared with the kernel and
	.BR rpc.gssd .
	A machine credential is established by
	.B rpc.gssd
	for the kernel when there is no user.
	Therefore
	.B rpc.gssd
	must already have the materials on hand to establish this credential
	without requiring user intervention.
	.P
	.B rpc.gssd
	searches the local system's keytab for a principal and key to use
	to establish the machine credential.
	By default,
	.B rpc.gssd
	assumes the file
	.I /etc/krb5.keytab
	contains principals and keys that can be used to obtain machine credentials.
	.P
	.B rpc.gssd
	searches in the following order for a principal to use.
	The first matching credential is used.
	For the search, <hostname> and <REALM> are replaced with the local
	system's hostname and Kerberos realm.
	.sp
	<HOSTNAME>$@<REALM>
	.br
	root/<hostname>@<REALM>
	.br
	nfs/<hostname>@<REALM>
	.br
	host/<hostname>@<REALM>
	.br
	root/<anyname>@<REALM>
	.br
	nfs/<anyname>@<REALM>
	.br
	host/<anyname>@<REALM>
	.sp
	The <anyname> entries match on the service name and realm, but ignore the hostname.
	These can be used if a principal matching the local host's name is not found.
	.P
	Note that the first principal in the search order is a user principal
	that enables Kerberized NFS when the local system is joined
	to an Active Directory domain using Samba.
	A password for this principal must be provided in the local system's keytab.
	.P
	You can specify another keytab by using the
	.B -k
	option if
	.I /etc/krb5.keytab
	does not exist or does not provide one of these principals.
	.SS Credentials for UID 0
	UID 0 is a special case.
	By default
	.B rpc.gssd
	uses the system's machine credentials for UID 0 accesses
	that require GSS authentication.
	This limits the privileges of the root user
	when accessing network resources that require authentication.
	.P
	Specify the
	.B -n
	option when starting
	.B rpc.gssd
	if you'd like to force the root user to obtain a user credential
	rather than use the local system's machine credential.
	.P
	When
	.B -n
	is specified,
	the kernel continues to request a GSS context established
	with a machine credential for NFSv4 operations,
	such as SETCLIENTID or RENEW, that manage state.
	If
	.B rpc.gssd
	cannot obtain a machine credential (say, the local system has
	no keytab), NFSv4 operations that require machine credentials will fail.
	.SS Encryption types
	A realm administrator can choose to add keys encoded in a number of different
	encryption types to the local system's keytab.
	For instance, a host/ principal might have keys for the
	.BR aes256-cts-hmac-sha1-96 ,
	.BR aes128-cts-hmac-sha1-96 ,
	.BR des3-cbc-sha1 ", and"
	.BR arcfour-hmac " encryption types."
	This permits
	.B rpc.gssd
	to choose an appropriate encryption type that the target NFS server
	supports.
	.P
	These encryption types are stronger than legacy single-DES encryption types.
	To interoperate in environments where servers support
	only weak encryption types,
	you can restrict your client to use only single-DES encryption types
	by specifying the
	.B -l
	option when starting
	.BR rpc.gssd .
	.SH OPTIONS
	.TP
	.B \-D
	The server name passed to GSSAPI for authentication is normally the
	name exactly as requested. e.g. for NFS
	it is the server name in the "servername:/path" mount request. Only if this
	servername appears to be an IP address (IPv4 or IPv6) or an
	unqualified name (no dots) will a reverse DNS lookup
	will be performed to get the canoncial server name.

	If
	.B \-D
	is present, a reverse DNS lookup will
	.I always
	be used, even if the server name looks like a canonical name. So it
	is needed if partially qualified, or non canonical names are regularly
	used.

	Using
	.B \-D
	can introduce a security vulnerability, so it is recommended that
	.B \-D
	not be used, and that canonical names always be used when requesting
	services.
	.TP
	.B -f
	Runs
	.B rpc.gssd
	in the foreground and sends output to stderr (as opposed to syslogd)
	.TP
	.B -n
	When specified, UID 0 is forced to obtain user credentials
	which are used instead of the local system's machine credentials.
	.TP
	.BI "-k " keytab
	Tells
	.B rpc.gssd
	to use the keys found in
	.I keytab
	to obtain machine credentials.
	The default value is
	.IR /etc/krb5.keytab .
	.TP
	.B -l
	When specified, restricts
	.B rpc.gssd
	to sessions to weak encryption types such as
	.BR des-cbc-crc .
	This option is available only when the local system's Kerberos library
	supports settable encryption types.
	.TP
	.BI "-p " path
	Tells
	.B rpc.gssd
	where to look for the rpc_pipefs filesystem. The default value is
	.IR /var/lib/nfs/rpc_pipefs .
	.TP
	.BI "-d " search-path
	This option specifies a colon separated list of directories that
	.B rpc.gssd
	searches for credential files. The default value is
	.IR /tmp:/run/user/%U .
	The literal sequence "%U" can be specified to substitue the UID
	of the user for whom credentials are being searched.
	.TP
	.B -M
	By default, machine credentials are stored in files in the first
	directory in the credential directory search path (see the
	.B -d
	option). When
	.B -M
	is set,
	.B rpc.gssd
	stores machine credentials in memory instead.
	.TP
	.B -v
	Increases the verbosity of the output (can be specified multiple times).
	.TP
	.B -r
	If the RPCSEC_GSS library supports setting debug level,
	increases the verbosity of the output (can be specified multiple times).
	.TP
	.BI "-R " realm
	Kerberos tickets from this
	.I 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.
	.TP
	.BI "-t " timeout
	Timeout, in seconds, for kernel GSS contexts. This option allows you to force
	new kernel contexts to be negotiated after
	.I 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.
	.SH SEE ALSO
	.BR rpc.svcgssd (8),
	.BR kerberos (1),
	.BR kinit (1),
	.BR krb5.conf (5)
	.SH AUTHORS
	.br
	Dug Song <dugsong@umich.edu>
	.br
	Andy Adamson <andros@umich.edu>
	.br
	Marius Aamodt Eriksen <marius@umich.edu>
	.br
	J. Bruce Fields <bfields@umich.edu>