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Autofs allows to automatically mount a filesystem when changing directory to the mounting point. The process is frozen while the file system is being mounted, and then the chdir() completes and enters the root of newly mounted filesystem.

I have been using autofs for several years, at first for mounting USB sticks, but now also for SMB shares and SSHFS. It is meant to be used for command-line users, I don't doubt that modern desktop environments provide the same features for GUI users.

The following describes my setup on a Debian Squeeze; there may be a more modern way of doing things (the original setup was on a Debian Sarge). I assume that you know how to administrate a Debian system (in other words, I won't be held responsible for damaging your system if you follow those instructions without understanding what they mean).

Autofs

The first step is to install the autofs, bsdutils, coreutils, lockfile-progs, gawk (or mawk), sed and the util-linux packages (most of those are probably installed already). The wget package (and command) allows me to write concise commands below, but feel free to use any other tool to download the necessary files from my web page.

USB Automounter

This setup allows to mount automatically any USB Mass Storage device, without the need to manually configure anything (as is the case in this Debian tutorial).

Edit as root the /etc/auto.master and add the following line:

/media  /etc/auto.usb  --timeout=3

Then run the following as root:

# mkdir -p /media
# mkdir -p /var/run/usbautomount
# mkdir -p /etc/usbautomount
# wget -O /etc/usbautomount/usbautomount http://weber.fi.eu.org/software/autofs/usbautomount
# chmod 755 /etc/usbautomount/usbautomount
# wget -O /etc/udev/usbautomount.rules http://weber.fi.eu.org/software/autofs/usbautomount.rules
# cd /etc/udev/rules.d
# ln -s ../usbautomount.rules z60_usbautomount.rules
# /etc/init.d/autofs restart

You then need to edit /etc/usbautomount/usbautomount to change references to mweber to your own username, and possibly change the mounting options (see line 142 of the script). I still use latin1 as a character encoding, so I want filenames to be automatically translated into latin1 for VFAT filesystems. Other filesystems are mounted without particular options.

The idea here is that when you plug a USB Mass Storage device into the computer, udev runs the usbautomount script that creates a name based on the USB device's vendor, model, instance (in the case the physical device contains more than one USB Mass Storage device, such as multi-card readers or smartphones with internal and removable flash memory) and partition number, creates a symlink in /var/run/usbautomount that points to a directory of the same name in /media. When you access the symlink, automount creates the directory in /media and mounts the file system from the USB device to that directory.

If you chdir() out of that directory, after 3 seconds automount unmounts the filesystem. If you chdir() into the directory again, automount mounts it again. The short timeout for automatic unmounting allows to unplug the device almost immediately after cd-ing out of the mount point (provided that there is no data to be written onto the device anymore). When you unplug the device, a script (generated by usbautomount when the device was plugged in) is run to remove the symlink from /var/run/usbautomount.

The cherry on the cake of this setup is the following:

$ mkdir $HOME/mnt
$ ln -s /var/run/usbautomount $HOME/mnt/USB

This way, $HOME/mnt/USB is automatically populated with links to the devices that you plug to your computer.

SMB/CIFS shares

The smbclient and cifs-utils packages need to be installed.

Run as root:

# mkdir -p /mnt/smb

Edit as root the /etc/auto.master and add the following line:

/mnt/smb  /etc/auto.smb  --timeout=10

(/etc/auto.smb comes with the autofs package).

Run this as your regular user:

$ ln -s /mnt/smb $HOME/mnt/smb

If you have an SMB/CIFS server named "foo" containing shares called "bar" and "quux", then going into /mnt/smb/foo will mount "bar" and "quux" in /mnt/smb/foo/bar and /mnt/smb/foo/quux. Automatic unmounting will happen 10 seconds after leaving /mnt/smb/foo.

If "foo" requires credentials (login and password), you can put them in /etc/auto.smb.foo as follows:

username = my_username
password = my_password

SSHFS

SSHFS itself requires some amount of setup. I will assume in the following that the client computer is called "local" and it accesses using SSH and SSHFS a remote computer called "remote" with user "user".

First, install the sshfs package. Then you need to create an SSH key for root@client, and authorize this key for user@remote. In the end, root@local must be able to log into user@remote using an SSH key instead of a password.

Once this is working, run as root:

# mkdir -p /mnt/ssh

Then edit /etc/auto.master as root and add the line:

/mnt/ssh  /etc/auto.ssh  --timeout=10,--ghost

Then create /etc/auto.ssh and add a line that looks like this (change the "user", and "remote" as needed):

remote -fstype=fuse,rw,nodev,nonempty,noatime,allow_other,max_read=65536 :sshfs\#user@remote\:

By default, SSHFS will mount the home directory of "user@remote" into /mnt/ssh/remote. If you need to acces another directory (e.g., /tmp), just append this path to the end of the line in /etc/auto.ssh:

remote-tmp -fstype=fuse,rw,nodev,nonempty,noatime,allow_other,max_read=65536 :sshfs\#user@remote\:/tmp

Finally, run this as your regular user:

$ ln -s /mnt/ssh $HOME/mnt/ssh

CDROM

It just came to my mind the other day that I could automount CD and DVD as well, but I haven't thought about the details yet. I remember the feature to be very annoying in Solaris twelve years ago, where the system was mounting the CD in a directory named after the label of the CD's filesystem, and never removing this directory. After mounting a few discs, the automount directory was filled with various directories with abtruse names, and you had to guess which one contained your data (I suppose mount would have told me what I wanted to know, I don't remeber if I tried that).