Autofs

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Revision as of 21:23, 14 March 2012 by MilanKnizek (Talk | contribs) (Configuration: Ehm, binding stops autofs to unmount the dirs. Soft-linking seems to work fine.)

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Introduction

This document outlines the procedure needed to set up AutoFS, a package that provides support for automounting removable media or network shares when they are inserted or accessed.

Installation

# pacman -S autofs
  • Load the autofs4 module as root:
# modprobe autofs4

Configuration

AutoFS uses template files for configuration which are located in /etc/autofs The main template is called auto.master, which can point to one or more other templates for specific media types.

  • Open the file /etc/autofs/auto.master with your favorite editor, you will see something similar to this:
/etc/autofs/auto.master
/var/autofs/misc	/etc/autofs/auto.misc
/var/autofs/net	/etc/autofs/auto.net

The first value on each line determines the base directory under which media are mounted, the second value which template to use. The default base path is /var/autofs, but you can change this to any other location you prefer. For instance:

/etc/autofs/auto.master
/media/misc     /etc/autofs/auto.misc     --timeout=5 --ghost
/media/net      /etc/autofs/auto.net      --timeout=60 --ghost

The optional parameter timeout sets the amount of seconds after which to unmount directories. The parameter ghost determines that configured mounts will always be shown, instead of only when they are inserted and accessed. This can be useful since you won't have to remember or guess the names of removable media and network shares.

The target directories have to exist on your system and need to be empty, since their contents will be swapped with the dynamically loaded media. This procedure is however non-destructive, so if you accidentally automount into a live directory you can just change the location in auto.master and restart AutoFS to regain the original contents.

If you still want to automount to a target non-empty directory and want to have the original files available even after the dynamically loaded directories are mounted, you can use autofs to mount them to another directory (e.g. /var/autofs/net) and create soft links

# ln -s /var/autofs/net/share_name /media/share_name
Note: Make sure there is an empty line on the end of template files (press Template:Keypress after last word). If there is no correct EOF line, the AutoFS daemon won't properly load.
  • Open the file /etc/nsswitch.conf and add an entry for automount:
automount: files
  • When you are done configuring, launch the AutoFS daemon as root:
# rc.d start autofs

To start the daemon on boot you can add autofs to the DAEMONS array in /etc/rc.conf, and autofs4 to the modules array in the same file.

Devices are now automatically mounted when they are accessed, they will remain mounted as long as you access them.

Removable media

  • Open /etc/autofs/auto.misc to add, remove or edit miscellaneous devices. For instance:
/etc/autofs/auto.misc
#kernel   -ro                                        ftp.kernel.org:/pub/linux
#boot     -fstype=ext2                               :/dev/hda1
usbstick  -fstype=auto,async,nodev,nosuid,umask=000  :/dev/sdb1
cdrom     -fstype=iso9660,ro                         :/dev/cdrom
#floppy   -fstype=auto                               :/dev/fd0

If you have a CD/DVD combo-drive you can change the cdrom line with -fstype=auto to have the media type autodetected.

NFS Network mounts

AutoFS provides a new way of automatically discovering and mounting NFS-shares on remote servers (the AutoFS network template in /etc/autofs/auto.net has been removed in autofs5). To enable automagic discovery and mounting of network shares from all accessible servers without any further configuration, you'll need to add the following to the /etc/autofs/auto.master file:

/net -hosts --timeout=60

Each host name needs to be resolveable, e.g. the name an IP address in /etc/hosts or via DNS and please make sure you have at least nfs-common installed and working.

For instance, if you have a remote server fileserver with an NFS share named /home/share, you can just access the share by typing:

# cd /net/fileserver/home/share
Note: Please note that ghosting, i.e. automatically creating directory placeholders before mounting shares is enabled by default, although AutoFS installation notes claim to remove that option from /etc/conf.d/autofs in order to start the AutoFS daemon.

The -hosts option uses a similar mechanism as the showmount command to detect remote shares. You can see the exported shares by typing:

# showmount <servername> -e 

Replacing <servername> with the name of your own server.

Samba

The Arch package does not provide any Samba or CIFS templates/scripts (23.07.2009), but the following should work for single shares:

add the following to /etc/autofs/auto.master

/media/[my_server] /etc/autofs/auto.[my_server]

and then create a file /etc/autofs/auto.[my_server]

[any_name] -fstype=cifs,[other_options] ://[remote_server]/[remote_share_name]

You can specify a user name and password to use with the share in the other_options section

[any_name] -fstype=cifs,username=[username],password=[password],[other_options] ://[remote_server]/[remote_share_name]
Note: Escape $, and other characters, with a backslash when neccessary.

FTP and SSH (with Fuse)

Remote FTP and SSH servers can be accessed seamlessly with AutoFS using FUSE, a virtual file system layer.

Remote FTP

First, install the curlftpfs package from the Community repository:

# pacman -S curlftpfs

Load the fuse module:

# modprobe fuse

Add fuse to the MODULES array in /etc/rc.conf to load it on each system boot.

Next, add a new entry for FTP servers in /etc/autofs/auto.master:

/media/ftp        /etc/autofs/auto.ftp    --timeout=60 --ghost

Create the file /etc/autofs/auto.ftp and add a server using the ftp://myuser:mypassword@host:port/path format:

servername -fstype=curl,rw,allow_other,nodev,nonempty,noatime    :ftp\://myuser\:mypassword\@remoteserver
Note: Your passwords are plainly visible for anyone that can run df (only for mounted servers) or view the file /etc/autofs/auto.ftp.

If you want slightly more security you can create the file ~root/.netrc and add the passwords there. Passwords are still plain text, but you can have mode 600, and df command will not show them (mounted or not). This method is also less sensitive to special characters (that else must be escaped) in the passwords. The format is:

machine remoteserver  
login myuser
password mypassword

The line in /etc/autofs/auto.ftp looks like this without user and password:

servername -fstype=curl,allow_other    :ftp\://remoteserver

Create the file /sbin/mount.curl with this code:

/sbin/mount.curl
 #! /bin/sh
 curlftpfs $1 $2 -o $4,disable_eprt

Create the file /sbin/umount.curl with this code:

/sbin/umount.curl
 #! /bin/sh
 fusermount -u $1

Set the permissions for both files:

# chmod 755 /sbin/mount.curl
# chmod 755 /sbin/umount.curl

After a restart your new FTP server should be accessible through /media/ftp/servername.

Remote SSH

These are basic instructions to access a remote filesystem over SSH with AutoFS.

Note: The example below does not use an ssh-passphrase to simplify the installation procedure, please note that this may be a security risk in case your local system gets compromised.

Install the sshfs package from the Extra repository:

# pacman -S sshfs

Load the fuse module:

# modprobe fuse

Add fuse to the MODULES array in /etc/rc.conf to load it on each system boot:

Install OpenSSH:

# pacman -S openssh

Generate an SSH keypair:

# ssh-keygen -t dsa

When the generator ask for a passphrase, just press Template:Keypress. Using SSH keys without a passphrase is less secure, yet running AutoFS together with passphrases poses some additional difficulties which are not (yet) covered in this article.

Next, copy the public key to the remote SSH server:

# ssh-copy-id -i /home/username/.ssh/id_dsa.pub username@remotehost

See that you can login to the remote server without entering a password:

# sudo ssh -i /home/username/.ssh/id_dsa username@remotehost
Note: The above command is needed to add the remote server to the root's list of known_hosts. Alternatively, hosts can be added to /etc/ssh/ssh_known_hosts.

Create a new entry for SSH servers in /etc/autofs/auto.master:

/media/ssh		/etc/autofs/auto.ssh	--timeout=60 --ghost

Create the file /etc/autofs/auto.ssh and add an SSH server:

/etch/autofs/auto.ssh
servername     -fstype=fuse,rw,allow_other,IdentityFile=/home/username/.ssh/id_dsa :sshfs\#username@host\:/

After a restart your SSH server should be accessible through /media/ssh/servername.

Troubleshooting and tweaks

This section contains a few solutions for common issues with AutoFS.

Using NIS

Version 5.0.5 of AutoFS has more advanced support for NIS. To use AutoFS together with NIS, add yp: in front of the template names in /etc/autofs/auto.master:

/home   yp:auto_home    --timeout=60 
/sbtn   yp:auto_sbtn    --timeout=60
+auto.master

On earlier versions of NIS (before 5.0.4), you should add nis to /etc/nsswitch.conf:

automount: files nis

Optional parameters

You can set parameters like timeout systemwide for all AutoFS media in /etc/conf.d/autofs:

  • Open the /etc/conf.d/autofs file and edit the daemonoptions line:
daemonoptions='--timeout=5'
  • To enable logging (default is no logging at all), add --verbose to the daemonoptions line in /etc/conf.d/autofs e.g.:
daemonoptions='--verbose --timeout=5'

After restarting the autofs daemon, verbose output is visible in /var/log/daemon.log.

Identify multiple devices

If you use multiple USB drives/sticks and want to easily tell them apart, you can use AutoFS to set up the mount points and Udev to create distinct names for your USB drives. See Map Custom Device Entries with udev for instructions on setting up Udev rules.

AutoFS permissions

If AutoFS isn't working for you, make sure that the permissions of the templates files are correct, otherwise AutoFS will not start. This may happen if you backed up your configuration files in a manner which did not preserve file modes. Here are what the modes should be on the configuration files:

  • 0644 - /etc/autofs/auto.master
  • 0644 - /etc/autofs/auto.media
  • 0644 - /etc/autofs/auto.misc
  • 0644 - /etc/conf.d/autofs

In general, scripts (like previous auto.net) should have executable (chown a+x filename) bits set and lists of mounts shouldn't.

If you are getting errors in /var/log/daemon.log similar to this, you have a permissions problem:

May  7 19:44:16 peterix automount[15218]: lookup(program): lookup for petr failed
May  7 19:44:16 peterix automount[15218]: failed to mount /media/cifs/petr

External links and resources

Alternatives to AutoFS