AutoFS is to mount volumes as they are needed and unmount them when
they are not in use. This is useful for sharing out home directories,
documentation, or applications to clients from a NAS cluster as well
as presenting standardized directory structures wherein the directory
structure of origin may not be standard. Both of which will be covered.
Our details for this are:
HOST (client): europa (10.0.7.90) HOST (NFS server): humboldt (10.0.7.125) OS: CentOS 6.2 Linux (RedHat EL derivative)
To start things off, I have a group "sci" and 2 users, "rfeynman" and
"pcherenkov". On this host, actual home directories are setup under
"/export/home", though our users' home directories are configured for
"/home":
europa [0] /bin/grep sci /etc/group sci:x:500: europa [0] /usr/bin/tail -2 /etc/passwd rfeynman:x:500:500:R. Feynman:/home/rfeynman:/bin/bash pcherenkov:x:501:500:P. Cherenkov:/home/pcherenkov:/bin/bash europa [0] /bin/ls -ld /home /export/home drwxr-xr-x. 5 root root 4096 Aug 23 14:47 /export/home/ drwxr-xr-x. 2 root root 4096 Aug 23 14:45 /home/ europa [0] /bin/ls -ld /home/* /export/home/* /bin/ls: cannot access /home/*: No such file or directory drwx------. 2 root root 16384 Aug 23 14:18 /export/home/lost+found/ drwx------. 2 pcherenkov sci 4096 Aug 23 14:47 /export/home/pcherenkov/ drwx------. 2 rfeynman sci 4096 Aug 23 14:47 /export/home/rfeynman/
As seen above, nothing exists under "/home", only "/export/home".
We could move the directories for our users or we could simply use AutoFS
to handle it for us. The default configuration options for AutoFS are
stored in "/etc/sysconfig/autofs". Initially, there will only be a few
entries defined and they are fairly self-explanatory:
europa [0] /bin/grep -v ^# /etc/sysconfig/autofs TIMEOUT=300 BROWSE_MODE="no" MOUNT_NFS_DEFAULT_PROTOCOL=4 USE_MISC_DEVICE="yes"
The "TIMEOUT" option above defines a value of 300 seconds, that being
how long the automounter will at least wait until unmounting an unused
mount under its control. Additionally, setting "BROWSE_MODE" to "no"
will prevent directory listings of potential AutoFS managed directory
structures until those directories have been mounted. Since AutoFS can
be manage by means other than local files (such as NIS maps), there is
a setting for it in "/etc/nsswitch.conf". For our purposes, we'll be
using local files for AutoFS configuration:
europa [0] /bin/grep automount /etc/nsswitch.conf automount: files
Getting back to our users, below, we add new local maps for "auto.home"
and "auto.info" to "/etc/auto.master":
europa [0] echo "/home /etc/auto.home" >> /etc/auto.master europa [0] echo "/opt /etc/auto.info" >> /etc/auto.master europa [0] /bin/grep -v ^# /etc/auto.master /misc /etc/auto.misc /net -hosts +auto.master /home /etc/auto.home /opt /etc/auto.info
In the above, we have our additions to the default entries. The format of
"auto.master" is (see man page: auto.master(5)):
mount_point map [options]
Next, we configure the "auto.home" map:
europa [0] echo "* -bind :/export/home/&" >> /etc/auto.home europa [0] /bin/cat /etc/auto.home * -bind :/export/home/&
Taken together with the "auto.home" entry in "/etc/auto.master", our
"auto.home" map entry says: for any user directory under "/export/home",
mount it under "/home" using mount option "bind" (see loopback mounts).
Since "autofs" is currently disabled, we need to enable and start it:
europa [0] /sbin/chkconfig --list autofs autofs 0:off 1:off 2:off 3:off 4:on 5:on 6:off europa [0] /sbin/chkconfig --level 3 autofs on europa [0] /sbin/service autofs start Starting automount: [ OK ]
The cool part about AutoFS is that it will only mount a volume as it
is needed. Since no AutoFS mounts are currently needed, "/home" is
still empty:
europa [0] /bin/ls -laF /home /export/home /export/home: total 32 drwxr-xr-x. 5 root root 4096 Aug 23 14:47 ./ drwxr-xr-x. 3 root root 4096 Aug 23 14:22 ../ drwx------. 2 root root 16384 Aug 23 14:18 lost+found/ drwx------. 2 pcherenkov sci 4096 Aug 23 14:47 pcherenkov/ drwx------. 2 rfeynman sci 4096 Aug 23 14:47 rfeynman/ /home: total 4 drwxr-xr-x. 2 root root 0 Aug 23 15:31 ./ dr-xr-xr-x. 26 root root 4096 Aug 23 15:31 ../
Since our users are configured to have their home directories under
"/home", by switching user to "rfeynman", "autofs" sees that the directory
for "/home/rfeynman" is needed and mounts it per the options we specified
in "auto.home":
europa [0] /bin/su - rfeynman [rfeynman@europa ~]$ pwd /home/rfeynman [rfeynman@europa ~]$ /bin/df -ah Filesystem Size Used Avail Use% Mounted on /dev/sda1 6.0G 1.6G 4.2G 27% / proc 0 0 0 - /proc sysfs 0 0 0 - /sys devpts 0 0 0 - /dev/pts tmpfs 467M 0 467M 0% /dev/shm /dev/sda3 1008M 98M 860M 11% /var none 0 0 0 - /proc/sys/fs/binfmt_misc /dev/sdb1 1020M 34M 935M 4% /export/home /export/home/rfeynman 1020M 34M 935M 4% /home/rfeynman [rfeynman@europa ~]$ /bin/ls -laF total 20 drwx------. 2 rfeynman sci 4096 Aug 23 14:47 ./ drwxr-xr-x. 3 root root 0 Aug 23 15:33 ../ -rw-r--r--. 1 rfeynman sci 18 Dec 2 2011 .bash_logout -rw-r--r--. 1 rfeynman sci 176 Dec 2 2011 .bash_profile -rw-r--r--. 1 rfeynman sci 124 Dec 2 2011 .bashrc -rw-r--r--. 1 rfeynman sci 121 Dec 7 2011 .kshrc [rfeynman@europa ~]$ /bin/ls -laF /home total 8 drwxr-xr-x. 3 root root 0 Aug 23 15:33 ./ dr-xr-xr-x. 26 root root 4096 Aug 23 15:31 ../ drwx------. 2 rfeynman sci 4096 Aug 23 14:47 rfeynman/ [rfeynman@europa ~]$ /bin/touch trashfile [rfeynman@europa ~]$ /bin/ls -li /home/rfeynman/trashfile /export/home/rfeynman/trashfile 21 -rw-r--r--. 1 rfeynman sci 0 Aug 23 15:35 /export/home/rfeynman/trashfile 21 -rw-r--r--. 1 rfeynman sci 0 Aug 23 15:35 /home/rfeynman/trashfile [rfeynman@europa ~]$ exit
In the output above, we see that "rfeynman" has full access to his
files and that his is the only directory currently under "/home".
Once we switch user to (or log in as) "pcherenkov", his directory is
also automatically mounted by the AutoFS 'automount' daemon.
europa [0] /bin/su - pcherenkov [pcherenkov@europa ~]$ /bin/df -ah Filesystem Size Used Avail Use% Mounted on /dev/sda1 6.0G 1.6G 4.2G 27% / proc 0 0 0 - /proc sysfs 0 0 0 - /sys devpts 0 0 0 - /dev/pts tmpfs 467M 0 467M 0% /dev/shm /dev/sda3 1008M 98M 860M 11% /var none 0 0 0 - /proc/sys/fs/binfmt_misc /dev/sdb1 1020M 34M 935M 4% /export/home /export/home/rfeynman 1020M 34M 935M 4% /home/rfeynman /export/home/pcherenkov 1020M 34M 935M 4% /home/pcherenkov [pcherenkov@europa ~]$ exit logout
While the volumes are mounted by "autofs", they are visible in
"/etc/mtab" and "/proc/mounts":
europa [0] /bin/grep home /etc/mtab /dev/sdb1 /export/home ext4 rw 0 0 /export/home/rfeynman /home/rfeynman none rw,bind 0 0 /export/home/pcherenkov /home/pcherenkov none rw,bind 0 0 europa [0] /bin/grep home /proc/mounts /dev/sdb1 /export/home ext4 rw,seclabel,relatime,barrier=1,data=ordered 0 0 /etc/auto.home /home autofs rw,relatime,fd=19,pgrp=3136,timeout=300,minproto=5,maxproto=5,\ indirect 0 0 /dev/sdb1 /home/rfeynman ext4 rw,seclabel,relatime,barrier=1,data=ordered 0 0 /dev/sdb1 /home/pcherenkov ext4 rw,seclabel,relatime,barrier=1,data=ordered 0 0
Remembering our default TIMEOUT option, even though "pcherenkov" has
logged out, the mounted volume (or filesystem in this case) will still
exist for a short while after it is no longer used. Below, I've switched
user back to "pcherenkov" to illustrate this. It takes about 330+ seconds
after logout for 'automount' to remove the "pcherenkov" home directory:
europa [0] /bin/grep ^TIMEOUT /etc/sysconfig/autofs TIMEOUT=300 europa [0] /bin/date ; /bin/ls /home ; /bin/su - pcherenkov -c "/usr/bin/whoami ; exit" ; \ > sleep 301 ; /bin/date ; /bin/ls /home ; \ > while : ; do /bin/date ; /bin/ls /home ; echo ; sleep 10 ; done Thu Aug 23 16:35:53 EDT 2012 rfeynman/ pcherenkov Thu Aug 23 16:40:54 EDT 2012 pcherenkov/ rfeynman/ Thu Aug 23 16:40:54 EDT 2012 pcherenkov/ rfeynman/ Thu Aug 23 16:41:04 EDT 2012 pcherenkov/ rfeynman/ Thu Aug 23 16:41:14 EDT 2012 pcherenkov/ rfeynman/ Thu Aug 23 16:41:24 EDT 2012 rfeynman/ ^C
One of the foremost reasons for using AutoFS is for dealing with NAS
volumes, such as NFS mounts. Having previously enabled rpcbind on europa
and set up an NFS server on humboldt (see nfs.linux), we can configure
our AutoFS map for "auto.info"
europa [0] /usr/bin/getent hosts humboldt-int 10.0.7.125 humboldt-int europa [0] /bin/grep info /etc/auto.master /opt /etc/auto.info europa [0] /bin/cat /etc/auto.info lhc-docs -ro,bg,intr humboldt-int:/export/lhc-docs man -ro,bg,intr humboldt-int:/export/man europa [0] /etc/init.d/autofs reload Reloading maps europa [0]
In the above "auto.info" configuration, both "lhc-docs" and "man" will
be automatically mounted by the AutoFS 'automount' daemon under "/opt"
as they are needed. The second column is simply standard NFS mount
options with the third column detailing the shared filesystem from the
NFS server. Switching back to user "rfeynman", we can see that nothing
initially exists under "/opt" until we need to access an AutoFS managed
directory structure:
[rfeynman@europa ~]$ pwd /home/rfeynman [rfeynman@europa ~]$ /bin/ls -al /opt total 4 drwxr-xr-x. 2 root root 0 Aug 23 17:31 . dr-xr-xr-x. 26 root root 4096 Aug 23 17:31 .. [rfeynman@europa ~]$ /bin/ls -al /opt/lhc-docs total 344 drwxr-xr-x. 2 4294967294 4294967294 4096 Aug 23 16:32 . drwxr-xr-x. 3 root root 0 Aug 23 17:40 .. -rw-r--r--. 1 4294967294 4294967294 1491 Aug 23 16:32 section.1 -rw-r--r--. 1 4294967294 4294967294 109208 Aug 23 16:29 section.2 -rw-r--r--. 1 4294967294 4294967294 45224 Aug 23 16:29 section.3 -rw-r--r--. 1 4294967294 4294967294 106232 Aug 23 16:30 section.4 -rw-r--r--. 1 4294967294 4294967294 76056 Aug 23 16:30 section.5 [rfeynman@europa ~]$ /usr/bin/head -10 /opt/lhc-docs/section.1 [http://public.web.cern.ch/public/en/lhc/lhc-en.html] The Large Hadron Collider Our understanding of the Universe is about to change... The Large Hadron Collider (LHC) is a gigantic scientific instrument near Geneva, where it spans the border between Switzerland and France about 100m underground. It is a particle accelerator used by physicists to study the smallest known particles – the fundamental building blocks of all things. It will revolutionise our understanding, from the minuscule
Our man directory, shared from "humboldt", is also available under /opt:
[rfeynman@europa ~]$ /usr/bin/gunzip -c /opt/man/man1/xxd.1.gz | \ > /usr/bin/groff -Tascii -man - | /usr/bin/head -20 XXD(1) XXD(1) NAME xxd - make a hexdump or do the reverse. SYNOPSIS xxd -h[elp] xxd [options] [infile [outfile]] xxd -r[evert] [options] [infile [outfile]] DESCRIPTION xxd creates a hex dump of a given file or standard input. It can a/bin/lso convert a hex dump back to its original binary form. Like uuencode(1) and uudecode(1) it allows the transmission of binary data in a `mail- safe' ASCII representation, but has the advantage of decoding to stan- dard output. Moreover, it can be used to perform binary file patching. OPTIONS
Since we've accessed both, they are now visible via a directory listing of
"/opt" as well as in a 'df' listing and a check of "/proc/mounts":
[rfeynman@europa ~]$ /bin/ls -al /opt total 12 drwxr-xr-x. 4 root root 0 Aug 23 17:43 . dr-xr-xr-x. 26 root root 4096 Aug 23 17:31 .. drwxr-xr-x. 2 4294967294 4294967294 4096 Aug 23 16:32 lhc-docs drwxr-xr-x. 20 4294967294 4294967294 4096 Aug 23 16:43 man [rfeynman@europa ~]$ /bin/df -h Filesystem Size Used Avail Use% Mounted on /dev/sda1 6.0G 1.6G 4.2G 27% / tmpfs 467M 0 467M 0% /dev/shm /dev/sda3 1008M 98M 860M 11% /var /dev/sdb1 1020M 34M 935M 4% /export/home humboldt-int:/export/lhc-docs 6.0G 1.6G 4.1G 28% /opt/lhc-docs humboldt-int:/export/man 6.0G 1.6G 4.1G 28% /opt/man [rfeynman@europa ~]$ /bin/egrep 'info|humboldt' /proc/mounts /etc/auto.info /opt autofs rw,relatime,fd=25,pgrp=4933,timeout=300,minproto=5,\ maxproto=5,indirect 0 0 humboldt-int:/export/lhc-docs /opt/lhc-docs nfs4 ro,relatime,vers=4,rsize=131072,\ wsize=131072,namlen=255,hard,proto=tcp,port=0,timeo=600,retrans=2,sec=sys,\ clientaddr=10.0.7.90,minorversion=0,local_lock=none,addr=10.0.7.125 0 0 humboldt-int:/export/man /opt/man nfs4 ro,relatime,vers=4,rsize=131072,wsize=131072,\ namlen=255,hard,proto=tcp,port=0,timeo=600,retrans=2,sec=sys,\ clientaddr=10.0.7.90,minorversion=0,local_lock=none,addr=10.0.7.125 0 0
see also:
Configuring AutoFS in FreeBSD
Remounting Part of an FS Elsewhere (loopback mounts)
Configuring NFS in Linux (nfs.linux)
