X-Git-Url: https://git.decadent.org.uk/gitweb/?p=nfs-utils.git;a=blobdiff_plain;f=utils%2Fexportfs%2Fexports.man;h=241b3afadd2964b09b93a38d0d05407e830ddc15;hp=2863feaeaa66960ebdeb0c7bf003cf5772459286;hb=7235a2164aabfd8dba1f7e1577047bda45053db0;hpb=8b7ad01b14df1e7529b9ba8a1ea17df0d6004ef9 diff --git a/utils/exportfs/exports.man b/utils/exportfs/exports.man index 2863fea..241b3af 100644 --- a/utils/exportfs/exports.man +++ b/utils/exportfs/exports.man @@ -1,106 +1,397 @@ -.TH EXPORTS 5 "11 August 1997" -.UC 5 +.\"@(#)exports.5" +.\" +.TH exports 5 "31 December 2009" .SH NAME -exports \- NFS file systems being exported -.SH SYNOPSIS -.B /etc/exports +exports \- NFS server export table .SH DESCRIPTION The file .I /etc/exports -serves as the access control list for file systems which may be -exported to NFS clients. It it used by both the NFS mount daemon, -.IR mountd (8) -and the NFS file server daemon -.IR nfsd (8). +contains a table of local physical file systems on an NFS server +that are accessible to NFS clients. +The contents of the file are maintained by the server's system +administrator. +.PP +Each file system in this table has a list of options and an +access control list. +The table is used by +.BR exportfs (8) +to give information to +.BR mountd (8). .PP The file format is similar to the SunOS .I exports -file, except that several additional options are permitted. Each line -contains a mount point and a list of machine or netgroup names allowed -to mount the file system at that point. An optional parenthesized list -of mount parameters may follow each machine name. Blank lines are -ignored, and a # introduces a comment to the end of the line. Entries may -be continued across newlines using a backslash. +file. Each line contains an export point and a whitespace-separated list +of clients allowed to mount the file system at that point. Each listed +client may be immediately followed by a parenthesized, comma-separated +list of export options for that client. No whitespace is permitted +between a client and its option list. +.PP +Also, each line may have one or more specifications for default options +after the path name, in the form of a dash ("\-") followed by an option +list. The option list is used for all subsequent exports on that line +only. +.PP +Blank lines are ignored. A pound sign ("#") introduces a comment to the +end of the line. Entries may be continued across newlines using a +backslash. If an export name contains spaces it should be quoted using +double quotes. You can also specify spaces or other unusual character in +the export name using a backslash followed by the character code as three +octal digits. +.PP +To apply changes to this file, run +.BR exportfs \-ra +or restart the NFS server. .PP .SS Machine Name Formats NFS clients may be specified in a number of ways: .IP "single host This is the most common format. You may specify a host either by an -abbreviated name recognizued be the resolver, the fully qualified domain +abbreviated name recognized be the resolver, the fully qualified domain name, or an IP address. -.IP "netgroups -NIS netgroups may be given as -.IR @group . -Only the host part of all -netgroup members is extracted and added to the access list. Empty host -parts or those containing a single dash (\-) are ignored. -.IP "wildcards -Machine names may contain the wildcard characters \fI*\fR and \fI?\fR. -This can be used to make the \fIexports\fR file more compact; for instance, -\fI*.cs.foo.edu\fR matches all hosts in the domain \fIcs.foo.edu\fR. However, -these wildcard characters do not match the dots in a domain name, so the -above pattern does not include hosts such as \fIa.b.cs.foo.edu\fR. .IP "IP networks You can also export directories to all hosts on an IP (sub-) network simultaneously. This is done by specifying an IP address and netmask pair as -.IR address/netmask . -.TP -.B =public -This is a special ``hostname'' that identifies the given directory name -as the public root directory (see the section on WebNFS in -.BR nfsd (8) -for a discussion of WebNFS and the public root handle). When using this -convention, -.B =public -must be the only entry on this line, and must have no export options -associated with it. Note that this does -.I not -actually export the named directory; you still have to set the exports -options in a separate entry. +.IR address/netmask +where the netmask can be specified in dotted-decimal format, or as a +contiguous mask length. +For example, either `/255.255.252.0' or `/22' appended +to the network base IPv4 address results in identical subnetworks with 10 bits of +host. Wildcard characters generally do not work on IP addresses, though they +may work by accident when reverse DNS lookups fail. +.IP "wildcards +Machine names may contain the wildcard characters \fI*\fR and \fI?\fR. +This can be used to make the \fIexports\fR file more compact; for instance, +\fI*.cs.foo.edu\fR matches all hosts in the domain +\fIcs.foo.edu\fR. As these characters also match the dots in a domain +name, the given pattern will also match all hosts within any subdomain +of \fIcs.foo.edu\fR. +.IP "netgroups +NIS netgroups may be given as +.IR @group . +Only the host part of each +netgroup members is consider in checking for membership. Empty host +parts or those containing a single dash (\-) are ignored. +.IP "anonymous +This is specified by a single +.I * +character (not to be confused with the +.I wildcard +entry above) and will match all clients. +'''.TP +'''.B =public +'''This is a special ``hostname'' that identifies the given directory name +'''as the public root directory (see the section on WebNFS in +'''.BR nfsd (8) +'''for a discussion of WebNFS and the public root handle). When using this +'''convention, +'''.B =public +'''must be the only entry on this line, and must have no export options +'''associated with it. Note that this does +'''.I not +'''actually export the named directory; you still have to set the exports +'''options in a separate entry. +'''.PP +'''The public root path can also be specified by invoking +'''.I nfsd +'''with the +'''.B \-\-public\-root +'''option. Multiple specifications of a public root will be ignored. .PP -The public root path can also be specified by invoking -.I nfsd -with the -.B \-\-public\-root -option. Multiple specifications of a public root will be ignored. +If a client matches more than one of the specifications above, then +the first match from the above list order takes precedence - regardless of +the order they appear on the export line. However, if a client matches +more than one of the same type of specification (e.g. two netgroups), +then the first match from the order they appear on the export line takes +precedence. +.SS RPCSEC_GSS security +You may use the special strings "gss/krb5", "gss/krb5i", or "gss/krb5p" +to restrict access to clients using rpcsec_gss security. However, this +syntax is deprecated; on linux kernels since 2.6.23, you should instead +use the "sec=" export option: +.TP +.IR sec= +The sec= option, followed by a colon-delimited list of security flavors, +restricts the export to clients using those flavors. Available security +flavors include sys (the default--no cryptographic security), krb5 +(authentication only), krb5i (integrity protection), and krb5p (privacy +protection). For the purposes of security flavor negotiation, order +counts: preferred flavors should be listed first. The order of the sec= +option with respect to the other options does not matter, unless you +want some options to be enforced differently depending on flavor. +In that case you may include multiple sec= options, and following options +will be enforced only for access using flavors listed in the immediately +preceding sec= option. The only options that are permitted to vary in +this way are ro, rw, no_root_squash, root_squash, and all_squash. .PP .SS General Options -.IR mountd " and " nfsd -understand the following export options: +.BR exportfs +understands the following export options: .TP .IR secure "\*d -This option requires that requests originate on an internet port less +This option requires that requests originate on an Internet port less than IPPORT_RESERVED (1024). This option is on by default. To turn it off, specify .IR insecure . .TP -.IR ro -Allow only read-only requests on this NFS volume. The default is to -allow write requests as well, which can also be made explicit by using +.IR rw +Allow both read and write requests on this NFS volume. The +default is to disallow any request which changes the filesystem. +This can also be made explicit by using the -.IR rw " option. +.IR ro " option. +.TP +.IR async +This option allows the NFS server to violate the NFS protocol and +reply to requests before any changes made by that request have been +committed to stable storage (e.g. disc drive). + +Using this option usually improves performance, but at the cost that +an unclean server restart (i.e. a crash) can cause data to be lost or +corrupted. + +.TP +.IR sync +Reply to requests only after the changes have been committed to stable +storage (see +.IR async +above). + +In releases of nfs-utils up to and including 1.0.0, the +.I async +option was the +default. In all releases after 1.0.0, +.I sync +is the default, and +.I async +must be explicitly requested if needed. +To help make system administrators aware of this change, +.B exportfs +will issue a warning if neither +.I sync +nor +.I async +is specified. +.TP +.IR no_wdelay +This option has no effect if +.I async +is also set. The NFS server will normally delay committing a write request +to disc slightly if it suspects that another related write request may be in +progress or may arrive soon. This allows multiple write requests to +be committed to disc with the one operation which can improve +performance. If an NFS server received mainly small unrelated +requests, this behaviour could actually reduce performance, so +.IR no_wdelay +is available to turn it off. +The default can be explicitly requested with the +.IR wdelay " option. +.TP +.IR nohide +This option is based on the option of the same name provided in IRIX +NFS. Normally, if a server exports two filesystems one of which is +mounted on the other, then the client will have to mount both +filesystems explicitly to get access to them. If it just mounts the +parent, it will see an empty directory at the place where the other +filesystem is mounted. That filesystem is "hidden". + +Setting the +.I nohide +option on a filesystem causes it not to be hidden, and an +appropriately authorised client will be able to move from the parent to +that filesystem without noticing the change. + +However, some NFS clients do not cope well with this situation as, for +instance, it is then possible for two files in the one apparent +filesystem to have the same inode number. + +The +.I nohide +option is currently only effective on +.I "single host +exports. It does not work reliably with netgroup, subnet, or wildcard +exports. + +This option can be very useful in some situations, but it should be +used with due care, and only after confirming that the client system +copes with the situation effectively. + +The option can be explicitly disabled with +.IR hide . +.TP +.IR crossmnt +This option is similar to +.I nohide +but it makes it possible for clients to move from the filesystem marked +with crossmnt to exported filesystems mounted on it. Thus when a child +filesystem "B" is mounted on a parent "A", setting crossmnt on "A" has +the same effect as setting "nohide" on B. +.TP +.IR no_subtree_check +This option disables subtree checking, which has mild security +implications, but can improve reliability in some circumstances. + +If a subdirectory of a filesystem is exported, but the whole +filesystem isn't then whenever a NFS request arrives, the server must +check not only that the accessed file is in the appropriate filesystem +(which is easy) but also that it is in the exported tree (which is +harder). This check is called the +.IR subtree_check . + +In order to perform this check, the server must include some +information about the location of the file in the "filehandle" that is +given to the client. This can cause problems with accessing files that +are renamed while a client has them open (though in many simple cases +it will still work). + +subtree checking is also used to make sure that files inside +directories to which only root has access can only be accessed if the +filesystem is exported with +.I no_root_squash +(see below), even if the file itself allows more general access. + +As a general guide, a home directory filesystem, which is normally +exported at the root and may see lots of file renames, should be +exported with subtree checking disabled. A filesystem which is mostly +readonly, and at least doesn't see many file renames (e.g. /usr or +/var) and for which subdirectories may be exported, should probably be +exported with subtree checks enabled. + +The default of having subtree checks enabled, can be explicitly +requested with +.IR subtree_check . + +From release 1.1.0 of nfs-utils onwards, the default will be +.I no_subtree_check +as subtree_checking tends to cause more problems than it is worth. +If you genuinely require subtree checking, you should explicitly put +that option in the +.B exports +file. If you put neither option, +.B exportfs +will warn you that the change is pending. + .TP -.I noaccess -This makes everything below the directory inaccessible for the named -client. This is useful when you want to export a directory hierarchy to -a client, but exclude certain subdirectories. The client's view of a -directory flagged with noaccess is very limited; it is allowed to read -its attributes, and lookup `.' and `..'. These are also the only entries -returned by a readdir. +.IR insecure_locks .TP -.IR link_relative -Convert absolute symbolic links (where the link contents start with a -slash) into relative links by prepending the necessary number of ../'s -to get from the directory containing the link to the root on the -server. This has subtle, perhaps questionable, semantics when the file -hierarchy is not mounted at its root. +.IR no_auth_nlm +This option (the two names are synonymous) tells the NFS server not to require authentication of +locking requests (i.e. requests which use the NLM protocol). Normally +the NFS server will require a lock request to hold a credential for a +user who has read access to the file. With this flag no access checks +will be performed. + +Early NFS client implementations did not send credentials with lock +requests, and many current NFS clients still exist which are based on +the old implementations. Use this flag if you find that you can only +lock files which are world readable. + +The default behaviour of requiring authentication for NLM requests can +be explicitly requested with either of the synonymous +.IR auth_nlm , +or +.IR secure_locks . .TP -.IR link_absolute -Leave all symbolic link as they are. This is the default operation. +.IR no_acl +On some specially patched kernels, and when exporting filesystems that +support ACLs, this option tells +.B nfsd +not to reveal ACLs to clients, so +they will see only a subset of actual permissions on the given file +system. This option is safe for filesystems used by NFSv2 clients and +old NFSv3 clients that perform access decisions locally. Current +NFSv3 clients use the ACCESS RPC to perform all access decisions on +the server. Note that the +.I no_acl +option only has effect on kernels specially patched to support it, and +when exporting filesystems with ACL support. The default is to export +with ACL support (i.e. by default, +.I no_acl +is off). + +'''.TP +'''.I noaccess +'''This makes everything below the directory inaccessible for the named +'''client. This is useful when you want to export a directory hierarchy to +'''a client, but exclude certain subdirectories. The client's view of a +'''directory flagged with noaccess is very limited; it is allowed to read +'''its attributes, and lookup `.' and `..'. These are also the only entries +'''returned by a readdir. +'''.TP +'''.IR link_relative +'''Convert absolute symbolic links (where the link contents start with a +'''slash) into relative links by prepending the necessary number of ../'s +'''to get from the directory containing the link to the root on the +'''server. This has subtle, perhaps questionable, semantics when the file +'''hierarchy is not mounted at its root. +'''.TP +'''.IR link_absolute +'''Leave all symbolic link as they are. This is the default operation. + +.TP +.IR mountpoint= path +.TP +.I mp +This option makes it possible to only export a directory if it has +successfully been mounted. +If no path is given (e.g. +.IR mountpoint " or " mp ) +then the export point must also be a mount point. If it isn't then +the export point is not exported. This allows you to be sure that the +directory underneath a mountpoint will never be exported by accident +if, for example, the filesystem failed to mount due to a disc error. + +If a path is given (e.g. +.IR mountpoint= "/path or " mp= /path) +then the nominated path must be a mountpoint for the exportpoint to be +exported. + +.TP +.IR fsid= num|root|uuid +NFS needs to be able to identify each filesystem that it exports. +Normally it will use a UUID for the filesystem (if the filesystem has +such a thing) or the device number of the device holding the +filesystem (if the filesystem is stored on the device). + +As not all filesystems are stored on devices, and not all filesystems +have UUIDs, it is sometimes necessary to explicitly tell NFS how to +identify a filesystem. This is done with the +.I fsid= +option. + +For NFSv4, there is a distinguished filesystem which is the root of +all exported filesystem. This is specified with +.I fsid=root +or +.I fsid=0 +both of which mean exactly the same thing. + +Other filesystems can be identified with a small integer, or a UUID +which should contain 32 hex digits and arbitrary punctuation. + +Linux kernels version 2.6.20 and earlier do not understand the UUID +setting so a small integer must be used if an fsid option needs to be +set for such kernels. Setting both a small number and a UUID is +supported so the same configuration can be made to work on old and new +kernels alike. + +.TP +.IR refer= path@host[+host][:path@host[+host]] +A client referencing the export point will be directed to choose from +the given list an alternative location for the filesystem. +(Note that the server must have a mountpoint here, though a different +filesystem is not required; so, for example, +.IR "mount --bind" " /path /path" +is sufficient.) +.TP +.IR replicas= path@host[+host][:path@host[+host]] +If the client asks for alternative locations for the export point, it +will be given this list of alternatives. (Note that actual replication +of the filesystem must be handled elsewhere.) + .SS User ID Mapping .PP -.I nfsd +.B nfsd bases its access control to files on the server machine on the uid and gid provided in each NFS RPC request. The normal behavior a user would expect is that she can access her files on the server just as she would @@ -118,138 +409,45 @@ and can be turned off with .IR no_root_squash . .PP By default, -.I nfsd -tries to obtain the anonymous uid and gid by looking up user -.I nobody -in the password file at startup time. If it isn't found, a uid and gid -of -2 (i.e. 65534) is used. These values can also be overridden by +'''.B nfsd +'''tries to obtain the anonymous uid and gid by looking up user +'''.I nobody +'''in the password file at startup time. If it isn't found, a uid and gid +.B exportfs +chooses a uid and gid +of 65534 for squashed access. These values can also be overridden by the .IR anonuid " and " anongid options. -.PP -In addition to this, -.I nfsd -lets you specify arbitrary uids and gids that should be mapped to user -nobody as well. Finally, you can map all user requests to the +'''.PP +'''In addition to this, +'''.B nfsd +'''lets you specify arbitrary uids and gids that should be mapped to user +'''nobody as well. +Finally, you can map all user requests to the anonymous uid by specifying the .IR all_squash " option. -.PP -For the benefit of installations where uids differ between different -machines, -.I nfsd -provides several mechanism to dynamically map server uids to client -uids and vice versa: static mapping files, NIS-based mapping, and -.IR ugidd -based -mapping. -.PP -.IR ugidd -based -mapping is enabled with the -.I map_daemon -option, and uses the UGID RPC protocol. For this to work, you have to run -the -.IR ugidd (8) -mapping daemon on the client host. It is the least secure of the three methods, -because by running -.IR ugidd , -everybody can query the client host for a list of valid user names. You -can protect yourself by restricting access to -.I ugidd -to valid hosts only. This can be done by entering the list of valid -hosts into the -.I hosts.allow -or -.I hosts.deny -file. The service name is -.IR ugidd . -For a description of the file's syntax, please read -.IR hosts_access (5). -.PP -Static mapping is enabled by using the -.I map_static -option, which takes a file name as an argument that describes the mapping. -NIS-based mapping queries the client's NIS server to obtain a mapping from -user and group names on the server host to user and group names on the -client. .PP Here's the complete list of mapping options: .TP .IR root_squash Map requests from uid/gid 0 to the anonymous uid/gid. Note that this does -not apply to any other uids that might be equally sensitive, such as user -.IR bin . +not apply to any other uids or gids that might be equally sensitive, such as +user +.IR bin +or group +.IR staff . .TP .IR no_root_squash Turn off root squashing. This option is mainly useful for diskless clients. .TP -.IR squash_uids " and " squash_gids -This option specifies a list of uids or gids that should be subject to -anonymous mapping. A valid list of ids looks like this: -.IP -.IR squash_uids=0-15,20,25-50 -.IP -Usually, your squash lists will look a lot simpler. -.TP .IR all_squash Map all uids and gids to the anonymous user. Useful for NFS-exported public FTP directories, news spool directories, etc. The opposite option -is +is .IR no_all_squash , which is the default setting. .TP -.IR map_daemon -This option turns on dynamic uid/gid mapping. Each uid in an NFS request -will be translated to the equivalent server uid, and each uid in an -NFS reply will be mapped the other way round. This option requires that -.IR rpc.ugidd (8) -runs on the client host. The default setting is -.IR map_identity , -which leaves all uids untouched. The normal squash options apply regardless -of whether dynamic mapping is requested or not. -.TP -.IR map_static -This option enables static mapping. It specifies the name of the file -that describes the uid/gid mapping, e.g. -.IP -.IR map_static=/etc/nfs/foobar.map -.IP -The file's format looks like this -.IP -.nf -.ta +3i -# Mapping for client foobar: -# remote local -uid 0-99 - # squash these -uid 100-500 1000 # map 100-500 to 1000-1500 -gid 0-49 - # squash these -gid 50-100 700 # map 50-100 to 700-750 -.fi -.TP -.IR map_nis -This option enables NIS-based uid/gid mapping. For instance, when -the server encounters the uid 123 on the server, it will obtain the -login name associated with it, and contact the NFS client's NIS server -to obtain the uid the client associates with the name. -.IP -In order to do this, the NFS server must know the client's NIS domain. -This is specified as an argument to the -.I map_nis -options, e.g. -.IP -.I map_nis=foo.com -.IP -Note that it may not be sufficient to simply specify the NIS domain -here; you may have to take additional actions before -.I nfsd -is actually able to contact the server. If your distribution uses -the NYS library, you can specify one or more NIS servers for the -client's domain in -.IR /etc/yp.conf . -If you are using a different NIS library, you may have to obtain a -special -.IR ypbind (8) -daemon that can be configured via -.IR yp.conf . -.TP .IR anonuid " and " anongid These options explicitly set the uid and gid of the anonymous account. This option is primarily useful for PC/NFS clients, where you might want @@ -258,6 +456,24 @@ export entry for .B /home/joe in the example section below, which maps all requests to uid 150 (which is supposedly that of user joe). +.SS Extra Export Tables +After reading +.I /etc/exports +.B exportfs +reads files under +.I /etc/exports.d. +directory as extra export tables. +.B exportfs +regards only a file which name is ended with +.I .exports +and +not started with +.I . +as an extra export file. A file which name +is not met this condition is just ignored. +The format for extra export tables is the same as +.I /etc/exports +. .IP .SH EXAMPLE .PP @@ -268,8 +484,9 @@ is supposedly that of user joe). /projects proj*.local.domain(rw) /usr *.local.domain(ro) @trusted(rw) /home/joe pc001(rw,all_squash,anonuid=150,anongid=100) -/pub (ro,insecure,all_squash) -/pub/private (noaccess) +/pub *(ro,insecure,all_squash) +/srv/www \-sync,rw server @trusted @external(ro) +'''/pub/private (noaccess) .fi .PP The first line exports the entire filesystem to machines master and trusty. @@ -279,28 +496,47 @@ and netgroups (this is the entry `@trusted'). The fourth line shows the entry for the PC/NFS client discussed above. Line 5 exports the public FTP directory to every host in the world, executing all requests under the nobody account. The -.I insecure +.I insecure option in this entry also allows clients with NFS implementations that -don't use a reserved port for NFS. The last line denies all NFS clients -access to the private directory. -.SH CAVEATS -Unlike other NFS server implementations, this -.I nfsd -allows you to export both a directory and a subdirectory thereof to -the same host, for instance -.IR /usr " and " /usr/X11R6 . -In this case, the mount options of the most specific entry apply. For -instance, when a user on the client host accesses a file in -.IR /usr/X11R6 , -the mount options given in the -.I /usr/X11R6 -entry apply. This is also true when the latter is a wildcard or netgroup -entry. +don't use a reserved port for NFS. +The sixth line exports a directory read-write to the machine 'server' +as well as the `@trusted' netgroup, and read-only to netgroup `@external', +all three mounts with the `sync' option enabled. +''' The last line denies all NFS clients +'''access to the private directory. +'''.SH CAVEATS +'''Unlike other NFS server implementations, this +'''.B nfsd +'''allows you to export both a directory and a subdirectory thereof to +'''the same host, for instance +'''.IR /usr " and " /usr/X11R6 . +'''In this case, the mount options of the most specific entry apply. For +'''instance, when a user on the client host accesses a file in +'''.IR /usr/X11R6 , +'''the mount options given in the +'''.I /usr/X11R6 +'''entry apply. This is also true when the latter is a wildcard or netgroup +'''entry. .SH FILES /etc/exports -.SH DIAGNOSTICS -An error parsing the file is reported using syslogd(8) as level NOTICE from -a DAEMON whenever nfsd(8) or mountd(8) is started up. Any unknown -host is reported at that time, but often not all hosts are not yet known -to named(8) at boot time, thus as hosts are found they are reported -with the same syslogd(8) parameters. +/etc/exports.d +.SH SEE ALSO +.BR exportfs (8), +.BR netgroup (5), +.BR mountd (8), +.BR nfsd (8), +.BR showmount (8). +'''.SH DIAGNOSTICS +'''An error parsing the file is reported using syslogd(8) as level NOTICE from +'''a DAEMON whenever +'''.BR nfsd (8) +'''or +'''.BR mountd (8) +'''is started up. Any unknown +'''host is reported at that time, but often not all hosts are not yet known +'''to +'''.BR named (8) +'''at boot time, thus as hosts are found they are reported +'''with the same +'''.BR syslogd (8) +'''parameters.