Mounting Devices through udev

Note

This method of hot-mounting a drive is superceded.

eSATA hot-mount drive setup

Note

This guide registers a BUFFALO External drive and mounts it at /home/mnt/backup.

1. The permanent logical mount point for the backup device will be /home/mnt/backup.

2. Display a terminal command line on the server console, or ssh to a server command shell.

3. Plug in the hot-pluggable device on a USB or eSATA port.

4. At the command prompt, type:

   dmesg | tail 20
   

5. Output similar to the following will be displayed:

   ...
   [ 5891.570018] ata6: link is slow to respond, please be patient (ready=0)
   [ 5893.250023] ata6: SATA link up 3.0 Gbps (SStatus 123 SControl 300)
   [ 5893.260131] ata6.00: ATA-6: BUFFALO External HDD, CC46, max UDMA/133
   [ 5893.260136] ata6.00: 1953525168 sectors, multi 0: LBA48
   [ 5893.271998] ata6.00: configured for UDMA/133
   [ 5893.272007] ata6: EH complete
   [ 5893.272117] scsi 5:0:0:0: Direct-Access     ATA      BUFFALO External CC46 PQ: 0 ANSI: 5
   [ 5893.272339] sd 5:0:0:0: Attached scsi generic sg3 type 0
   [ 5893.272669] sd 5:0:0:0: [sdc] 1953525168 512-byte logical blocks: (1.00 TB/931 GiB)
   [ 5893.272727] sd 5:0:0:0: [sdc] Write Protect is off
   [ 5893.272731] sd 5:0:0:0: [sdc] Mode Sense: 00 3a 00 00
   [ 5893.272762] sd 5:0:0:0: [sdc] Write cache: enabled, read cache: enabled, doesn''t support DPO or FUA
   [ 5893.272939]  sdc: sdc1 < sdc5 >
   [ 5893.293515] sd 5:0:0:0: [sdc] Attached SCSI disk
   

6. This shows a BUFFALO External device as sdc. Enumerate the system device information for sdc with the command:

   udevadm info --name=sdc --attribute-walk
   

7. Now scroll up the output to find the BUFFALO External parent device section. Note the subsystem, model, and state:

   looking at parent device '/devices/pci0000:00/0000:00:1f.2/host5/target5:0:0/5:0:0:0':
      KERNELS=="5:0:0:0"
      SUBSYSTEMS=="scsi"
      DRIVERS=="**sd**"
      ATTRS{device_blocked}=="0"
      ATTRS{type}=="0"
      ATTRS{scsi_level}=="6"
      ATTRS{vendor}=="ATA     "
      ATTRS{model}=="BUFFALO External"
      ATTRS{rev}=="CC46"
      ATTRS{state}=="running"
      ...
   

8. Add a udev rule in directory /etc/udev/rules.d/ to establish a mount for the device. We chose the filename:

   /etc/udev/rules.d/20-buffalo.rules
   

9. Edit the file and insert the rule. Our data for the command, based on the attributes above and the specified mount point, is:

   KERNEL=="sd?", SUBSYSTEMS=="scsi", ATTRS{model}=="BUFFALO External", ATTRS{state}=="running", RUN+="/bin/mount /dev/%k5 /home/mnt/backup"
   

10. After saving the rule, and with the device connected, verify the rule with the command:

    sudo reload udev
    sudo udevadm test /block/sdc
    

11. The command output should be similar to the following:

    ...
    udevadm_test: ID_ATA_SATA=1
    udevadm_test: ID_ATA_SATA_SIGNAL_RATE_GEN2=1
    udevadm_test: ID_ATA_SATA_SIGNAL_RATE_GEN1=1
    udevadm_test: ID_SCSI_COMPAT=SATA_BUFFALO_Externa_6VPB88MX
    udevadm_test: ID_PATH=pci-0000:00:1f.2-scsi-2:0:0:0
    udevadm_test: ID_PART_TABLE_TYPE=dos
    udevadm_test: UDISKS_PRESENTATION_NOPOLICY=0
    udevadm_test: UDISKS_PARTITION_TABLE=1
    udevadm_test: UDISKS_PARTITION_TABLE_SCHEME=mbr
    udevadm_test: UDISKS_PARTITION_TABLE_COUNT=2
    udevadm_test: UDISKS_ATA_SMART_IS_AVAILABLE=1
    udevadm_test: run: '/bin/mount /dev/sdc5 /home/mnt/backup'
    udevadm_test: run: '/lib/udev/hdparm'
    udevadm_test: run: 'socket:@/org/freedesktop/hal/udev_event'
    

12. Now unplug the eSATA or USB cable, and then plug it back into the device.

13. Run the command mount and look for the device in the command output, as for example the following:

    /dev/mapper/ddf1_aaltsys1 on / type ext4 (rw,errors=remount-ro)
    ...
    none on /var/lib/ureadahead/debugfs type debugfs (rw,relatime)
    /dev/mapper/ddf1_aaltsys6 on /home type ext4 (rw,usrquota,grpquota,acl)
    rpc_pipefs on /var/lib/nfs/rpc_pipefs type rpc_pipefs (rw)
    nfsd on /proc/fs/nfsd type nfsd (rw)
    /dev/sdc5 on /home/mnt/backup type fuseblk (rw,nosuid,nodev,allow_other,blksize=4096)
    

The device is mounted and ready. Now it may be hot connected and disconnected, and it will auto-mount on connection.

Disconnecting a hot-mounted drive

Unmount a device before disconnecting it. In this example, the unmount command would be:

umount /home/mnt/backup

Warning

Before disconnecting a hot-mounted device it must be unmounted. Otherwise the device may become corrupted or unusable.

References

1. We found the following guide useful: http://cdfx.penguins-on-hudson.com/2010/01/20/automount-removable-devices-on-ubuntu-servers/. Be aware that all the udev command syntax has changed since the guide was written, as the following table shows.

Command in Penguins Guide	Current Command Syntax Equivalent
udevinfo -a -p /sys/block/sdb	udevadm info –name=sdb –attribute-walk
sudo udevcontrol reload_rules	sudo reload udev
udevtest /sys/block/sdb/sdb1 usb	sudo udevadm test /block/sdb