Is udev all that is needed for automounting?

Question

Hi All,
As soon as my new hard drive shows, I'm planning on installing Arch on it, and I was hoping to clear up some confusion before then. While i'm not necessarily a linux noob, gnome has covered up alot of stuff that I'll need to know for the switch to arch so I am pretty nooby to the stuff that happens deep down in the bowels of my computer. I've been reading around about udev, and it appears that it will handle all device recognition/automounting/ect. If so, do I need hotplug, hal, hwd, ect, ect?
Right now I am running ubuntu with fluxbox, and gnome-volume-manager takes care of automounting. This works allright, but I would much rather not install gnome along with arch. I've found plenty of articles about setting up udev, and would like to use it exclusivly if possable due to it's ease of use (the keys seem simple enough) and reliability. I am, however, a little confused as to what it actually does when something is connected to the system. Will udev actually reconize that say, a pendrive has been inserted, or does some other program take care of recognition while udev takes care of mounting? Also, I'd still like to use fstab for mounting my static HDD's at boot, does the kernel actually use this file, or do I need another program for this functionality?

Answer 1

My latest udev rules for usb sticks or usb hard disks automounting (/etc/udev/rules.d/010.udev.rules):
KERNEL=="sd[b-z]", NAME="%k", SYMLINK+="usbhd-%k", GROUP="users", OPTIONS="last_rule"
ACTION=="add", KERNEL=="sd[b-z][0-9]", SYMLINK+="usbhd-%k", GROUP="users", NAME="%k"
ACTION=="add", KERNEL=="sd[b-z][0-9]", RUN+="/bin/mkdir -p /media/usbhd-%k"
ACTION=="add", KERNEL=="sd[b-z][0-9]", RUN+="/bin/ln -s /media/usbhd-%k /mnt/usbhd-%k"
ACTION=="add", KERNEL=="sd[b-z][0-9]", PROGRAM=="/lib/udev/vol_id -t %N", RESULT=="vfat", RUN+="/bin/mount -t vfat -o rw,noauto,sync,dirsync,noexec,nodev,noatime,dmask=000,fmask=111 /dev/%k /media/usbhd-%k", OPTIONS="last_rule"
ACTION=="add", KERNEL=="sd[b-z][0-9]", RUN+="/bin/mount -t auto -o rw,noauto,sync,dirsync,noexec,nodev,noatime /dev/%k /media/usbhd-%k", OPTIONS="last_rule"
ACTION=="remove", KERNEL=="sd[b-z][0-9]", RUN+="/bin/rm -f /mnt/usbhd-%k"
ACTION=="remove", KERNEL=="sd[b-z][0-9]", RUN+="/bin/umount -l /media/usbhd-%k"
ACTION=="remove", KERNEL=="sd[b-z][0-9]", RUN+="/bin/rmdir /media/usbhd-%k", OPTIONS="last_rule"
Mr Green reminded me about path change for vol_id which is now /lib/udev/vol_id (was /sbin/vol_id). Tnx. I've changed it in the above rules.
I have SATA hard disk in my notebook (/dev/sda) so I have to use sd[b-z] for removable media. /dev/sda is mounted normally via fstab. If you don't have any fixed sd* devices in your fstab you can use sb[a-z] everywhere.
How does udev know when you're about to pull out your USB-stick?
It doesn't :-) As you can see I'm using mount with several options like sync and dirsync and "lazy umount".
Usinc sync and dirsync sometimes slows down transfer speed but it's safer than async. Basically it saves data to the device instantly so there is little risk of losing data when you unplug usb stick.
When you first plug a device these rules create subdirectory in /media, mount every partition found on it to it's own subdirectory and make symlinks from /mnt to /media for each device/partition - this is not required but it's good to have them accessible from both /mnt and /media.
These rules can detect vfat partition and use different mount options (dmask,fmask) which allows every user to access vfat partition (read and write).
Any other partition type is mounted with general mount options.
I have an usb stick with 2 partitions: one vfat and one reiserfs. They both work well with these rules.
When you unplug the device remove event is generated, /dev/sdX is removed by udev and then the rules umount all partitions with lazy umount (which prevents the panic of applications that still have any file or directory opened from any of umounted partitions).
Next all directories in /media and symlinks in /mnt are removed.
This way all you need for automounting is udev rules (no need for fstab items etc.) and you don't need to know in advance how many partitions and what type of filesystems are used.
I'm using this for most of my linux computers and so far it works quite well. Of course it has some drawbacks (like slower speed) but for me this is clean and simple and I don't have to worry about every ivman/whatever update ;-)