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NFS 서버 설정 (/etc/exports)
NFS(Network File System)
- 1984년 Sun Microsystems 사에서 개발한 프로토콜
- TCP/IP 네트워크상에서 다른 컴퓨터의 파일 시스템을 마운트하고 공유한다.
- 상대방의 파일 시스템 일부를 마치 자기 자신의 디렉터리인 것처럼 사용 할 수 있게 해준다.
- NIS와 더불어 RPC(Remote Procedure Call) 기반으로 작동한다.
- 해당 서비스를 해주는 rpcbind(구 portmap) 데몬을 먼저 실행시켜야 한다.
- 사용이 편리한 대신, 보안에 상당히 미약하기 때문에 주의해서 사용해야 한다.
NFS 관련 주요 RPM 패키지
- NFS 서버를 구축하려면 다음과 같이 2개의 패키지를 설치해야 한다.
- rpcbind
- RPC 기반 연결을 위해 필요한 패키지
- rpcbind, rpcinfo 등 포함
- nfs-utils
- NFS 서버 관련 패키지
- 관련 데몬 및 명령어 포함
- rpcbind
NFS 서버의 설정의 개요
- NFS 서버의 접근 제어
- /etc/exports 파일에서 설정
- 특정 디렉터리에 rw 옵션을 지정하는 경우, 리눅스의 디렉터리 퍼미션에도 rw 권한이 있는지 반드시 확인해야 한다.
- /etc/exports 파일에서 설정
- 데몬 스크립트인 rpcbind, nfs-server 를 실행하면 사용이 가능하다.
NFS 서버 설정 순서
① 접근 관련 설정
# vi /etc/exports
② 관련 데몬 실행
- 기본적으로 관련 데몬 스크립트는 nfs-server.service 이지만, nfs-server 라는 스크립트도 제공한다.
- 변동 사항이 있는 경우
- systemctl start nfs-server 스크립트 전에 systemctl daemon-reload 명령의 실행을 요구하기도 한다.
- 관련 메시지가 발생하면 먼저 실행하도록 한다.
- systemctl start nfs-server 스크립트 전에 systemctl daemon-reload 명령의 실행을 요구하기도 한다.
# systemctl start rpcbind
# systemctl start nfs-server
③ 서버 동작과 관련 메시지 확인
- NFS 서버 동작 오류 시에 매우 유용하다.
- 성공적으로 시작했을 경우에도 관련 정보를 자세하게 확인할 수 있다.
# systemctl -l status nfs-server
④ 관련 서버 동작의 확인
- ps 명령으로 관련 데몬이 정상적으로 동작하는지 확인한다.
# ps aux | egrep 'rpcinfo | nfs-server'
⑤ NFS 서버의 재시작
- NFS 서버 관련 설정을 변경했을 경우에는 관련 데몬을 재시작해야 한다.
# systemctl restart nfs-server
⑥ 부팅 시 NFS 관련 서버 활성화
# systemctl enable rpcinfo nfs-server
환경 설정 파일 : /etc/exports
- /etc/exports 파일 설정
- 줄 단위로 외부에 공유할 디렉터리를 입력
- 공백([TAB])으로 구분하여 허가 할 호스트 지정 및 옵션 기입
- 허가 할 호스트
- IP 주소
- 도메인
- /etc/hosts에 설정한 호스트명
- NIS 에서 설정한 그룹명
- 와일드 카드로 ‘모두’ 라는 의미의 * 사용 가능
설정법
공유_할_디렉터리 허가할_호스트(옵션) [허가할_호스트(옵션) ...]
주요 옵션
| 옵션 | 설명 |
| ro | 읽기 전용으로 지정하는 옵션 (기본값) |
| rw | 읽기 및 쓰기가 가능하도록 지정하는 옵션 |
| root_squash | - NFS 클라이언트에서 접근하는 root 사용자를 무시하고, 서버상의 nobody(또는 nfsnobody)로 매핑시키는 옵션 (기본값) - 일반 사용자의 권한은 그대로 인정된다. |
| no_root_squash | NFS 클라이언트에서 접근하는 root 사용자를 무시하지 않고, root으로 인정한다. |
| all_squash | root를 포함하여 모든 사용자의 권한을 nobody(또는 nfsnobody)로 매핑시킨다. |
| no_subtree_check | 하위 디렉터리를 검사하지 못하도록 할 때 설정 |
| secure | - 포트 번호가 1024 이하인 요청만 허가할 때 사용한다. - 기본값으로 설정되어 있다. - 반대 설정 : insecure |
| sync | - 변경 사항이 안정적으로 저장된 경우에만 관련 요청에 응답하도록 한다. - 기본값으로 설정되어 있다. |
| async | - 쓰기가 설정된 디스크 스토리지에 사용하면 유용한 옵션 - 데이터 변경(Data Corruption)에 대비히 비동기적 처리를 할 때 사용 |
| anonuid | 접근하는 사용자 권한을 지정하는 uid로 매핑시킬 때 사용 |
| anongid | 접근하는 그룹 권한을 지정하는 gid로 매핑시킬 때 사용 |
설정 예
/nfsdata 192.168.5.13
/nfdsdata1 192.168.5.0/255.255.255.0(rw, root_squash)
/nfdsdata2 192.168.12.0/24(rw, no_root_squash)
/nfdsdata1 *.hankuk.ac.kr(rw, all_squash)
/ master(rw) trusty(rw, no_root_squash)
/home/starrykss linux120(rw, all_squash, anonuid=500, anongid=500)
NFS 클라이언트에서 사용법
- NFS 클라이언트에서는 mount 명령을 이용하여 NFS 서버의 파일 시스템을 이용할 수 있다.
- 부팅할 때 마운트하여 사용하려면 /etc/fstab 파일에 등록하면 된다.
(1) mount 및 mount.nfs 명령 이용하기
사용 예
- 192.168.5.13의 /nfsdata를 /mnt 디렉터리로 마운트
# mount -t nfs 192.168.5.13:/nfsdata /mnt
- 192.168.5.13의 /nfsdata를 /mnt 디렉터리로 마운트
# mount.nfs 192.168.5.13:/nfsdata /mnt
(2) /etc/fstab 등록하기
설정 예
# vi /etc/fstab192.168.5.13:/nfsdata /mnt nfs timeo=15,soft,retrans=3 0 0
주요 옵션
| 옵션 | 설명 |
| timeo | - RPC 타임아웃이 발생된 후에 첫 번째 재전송 요구를 보낼 때의 시간 - 단위 : 1/10초 |
| retrans | 타임아웃이 발생된 후에 재전송 요구의 횟수를 지정한다. |
| soft | NFS 서버 요청에 실패하면 retrans에 설정한 횟수만큼 재요청을 시도한다. |
| hard | - NFS 서버 요청에 실패하면 무한정 재시도한다. - 특별히 옵션을 명시하지 않으면 기본적으로 적용된다. |
| rsize | NFS 서버로부터 읽어 들이는 바이트 값 지정 |
| wsize | NFS 서버에 쓸 때 적용되는 바이트 값 지정 |
| fg | Foreground 형태로 마운트를 시도하고, 실패하면 마운트를 중단한다. |
| bg | 첫 번째 마운트에 실패하면 백그라운드 형태로 다시 시도한다. |
문제 해결 전략
- NFS 서버 설정 파일의 내용을 채우는 문제가 출제된다.
- NFS 서버의 설정 파일은 /etc/exports 이며, 이 파일에 대한 정보는 'man exports' 명령을 사용하여 확인한다.
더보기
$ man exportsexports(5) File Formats Manual exports(5)
NAME
exports - NFS server export table
DESCRIPTION
The file /etc/exports 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 admin‐
istrator.
Each file system in this table has a list of options and an access control list. The table is
used by exportfs(8) to give information to mountd(8).
The file format is similar to the SunOS exports 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.
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.
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.
To apply changes to this file, run exportfs -ra or restart the NFS server.
Machine Name Formats
NFS clients may be specified in a number of ways:
single host
You may specify a host either by an abbreviated name recognized be the resolver, the fully
qualified domain name, an IPv4 address, or an IPv6 address. IPv6 addresses must not be
inside square brackets in /etc/exports lest they be confused with character-class wildcard
matches.
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 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 iden‐
tical subnetworks with 10 bits of host. IPv6 addresses must use a contiguous mask length
and must not be inside square brackets to avoid confusion with character-class wildcards.
Wildcard characters generally do not work on IP addresses, though they may work by accident
when reverse DNS lookups fail.
wildcards
Machine names may contain the wildcard characters * and ?, or may contain character class
lists within [square brackets]. This can be used to make the exports file more compact;
for instance, *.cs.foo.edu matches all hosts in the domain cs.foo.edu. As these characters
also match the dots in a domain name, the given pattern will also match all hosts within
any subdomain of cs.foo.edu.
netgroups
NIS netgroups may be given as @group. Only the host part of each netgroup members is con‐
sider in checking for membership. Empty host parts or those containing a single dash (-)
are ignored.
anonymous
This is specified by a single * character (not to be confused with the wildcard entry
above) and will match all clients.
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.
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:
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 protec‐
tion), 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.
General Options
exportfs understands the following export options:
secure 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 insecure.
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 ro
option.
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.
sync Reply to requests only after the changes have been committed to stable storage (see async
above).
In releases of nfs-utils up to and including 1.0.0, the async option was the default. In
all releases after 1.0.0, sync is the default, and async must be explicitly requested if
needed. To help make system administrators aware of this change, exportfs will issue a
warning if neither sync nor async is specified.
no_wdelay
This option has no effect if async is also set. The NFS server will normally delay commit‐
ting 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
no_wdelay is available to turn it off. The default can be explicitly requested with the
wdelay option.
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 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 nohide option is currently only effective on 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 for NFSv2 and NFSv3 with hide.
This option is not relevant when NFSv4 is use. NFSv4 never hides subordinate filesystems.
Any filesystem that is exported will be visible where expected when using NFSv4.
crossmnt
This option is similar to nohide but it makes it possible for clients to access all
filesystems mounted on a filesystem marked with crossmnt. Thus when a child filesystem "B"
is mounted on a parent "A", setting crossmnt on "A" has a similar effect to setting
"nohide" on B.
With nohide the child filesystem needs to be explicitly exported. With crossmnt it need
not. If a child of a crossmnt file is not explicitly exported, then it will be implicitly
exported with the same export options as the parent, except for fsid=. This makes it
impossible to not export a child of a crossmnt filesystem. If some but not all subordinate
filesystems of a parent are to be exported, then they must be explicitly exported and the
parent should not have crossmnt set.
The nocrossmnt option can explictly disable crossmnt if it was previously set. This is
rarely useful.
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 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 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 sub‐
tree_check.
From release 1.1.0 of nfs-utils onwards, the default will be no_subtree_check as sub‐
tree_checking tends to cause more problems than it is worth. If you genuinely require sub‐
tree checking, you should explicitly put that option in the exports file. If you put nei‐
ther option, exportfs will warn you that the change is pending.
insecure_locks
no_auth_nlm
This option (the two names are synonymous) tells the NFS server not to require authentica‐
tion 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 cur‐
rent 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 auth_nlm, or secure_locks.
mountpoint=path
mp This option makes it possible to only export a directory if it has successfully been
mounted. If no path is given (e.g. 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. mountpoint=/path or mp=/path) then the nominated path must be a
mountpoint for the exportpoint to be exported.
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 fsid= option.
For NFSv4, there is a distinguished filesystem which is the root of all exported filesys‐
tem. This is specified with fsid=root or 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.
nordirplus
This option will disable READDIRPLUS request handling. When set, READDIRPLUS requests from
NFS clients return NFS3ERR_NOTSUPP, and clients fall back on READDIR. This option affects
only NFSv3 clients.
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, mount --bind /path
/path is sufficient.)
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 else‐
where.)
pnfs This option enables the use of the pNFS extension if the protocol level is NFSv4.1 or
higher, and the filesystem supports pNFS exports. With pNFS clients can bypass the server
and perform I/O directly to storage devices. The default can be explicitly requested with
the no_pnfs option.
security_label
With this option set, clients using NFSv4.2 or higher will be able to set and retrieve
security labels (such as those used by SELinux). This will only work if all clients use a
consistent security policy. Note that early kernels did not support this export option,
and instead enabled security labels by default.
User ID Mapping
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 on a normal file system. This requires that the same uids and gids are
used on the client and the server machine. This is not always true, nor is it always desirable.
Very often, it is not desirable that the root user on a client machine is also treated as root
when accessing files on the NFS server. To this end, uid 0 is normally mapped to a different id:
the so-called anonymous or nobody uid. This mode of operation (called `root squashing') is the
default, and can be turned off with no_root_squash.
By default, exportfs chooses a uid and gid of 65534 for squashed access. These values can also be
overridden by the anonuid and anongid options. Finally, you can map all user requests to the
anonymous uid by specifying the all_squash option.
Here's the complete list of mapping options:
root_squash
Map requests from uid/gid 0 to the anonymous uid/gid. Note that this does not apply to any
other uids or gids that might be equally sensitive, such as user bin or group staff.
no_root_squash
Turn off root squashing. This option is mainly useful for diskless clients.
all_squash
Map all uids and gids to the anonymous user. Useful for NFS-exported public FTP directo‐
ries, news spool directories, etc. The opposite option is no_all_squash, which is the
default setting.
anonuid and anongid
These options explicitly set the uid and gid of the anonymous account. This option is pri‐
marily useful for PC/NFS clients, where you might want all requests appear to be from one
user. As an example, consider the export entry for /home/joe in the example section below,
which maps all requests to uid 150 (which is supposedly that of user joe).
Extra Export Tables
After reading /etc/exports exportfs reads files in the /etc/exports.d directory as extra export
tables. Only files ending in .exports are considered. Files beginning with a dot are ignored.
The format for extra export tables is the same as /etc/exports
EXAMPLE
# sample /etc/exports file
/ master(rw) trusty(rw,no_root_squash)
/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)
/srv/www -sync,rw server @trusted @external(ro)
/foo 2001:db8:9:e54::/64(rw) 192.0.2.0/24(rw)
/build buildhost[0-9].local.domain(rw)
The first line exports the entire filesystem to machines master and trusty. In addition to write
access, all uid squashing is turned off for host trusty. The second and third entry show examples
for wildcard hostnames 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 insecure option in this entry
also allows clients with NFS implementations that 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 sev‐
enth line exports a directory to both an IPv6 and an IPv4 subnet. The eighth line demonstrates a
character class wildcard match.
FILES
/etc/exports /etc/exports.d
SEE ALSO
exportfs(8), netgroup(5), mountd(8), nfsd(8), showmount(8).
31 December 2009 exports(5)
문제 유형
① 조건에 맞게 설정 파일에 내용을 추가하는 문제
- 기본적인 설정법은 '공유할_디렉터리 허가할_호스트(옵션) [허가할_호스트(옵션) ...]' 형식이다.
/etc/exports
( /data/nfs ) 192.168.10.10( ( rw ), ( root_squash ) )# vi ( /etc/exports )
( /data/presales *.example.com(rw, no_root_squash) )# vi /etc/exports
/nfs_share ( 192.168.5.0/24 )(rw, ( no_root_squash ))
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