I wanted to easily synchronize my backup directory to an external USB-disk by simply inserting the disk. Since udev is in charge of managing devices in Linux, I'll let it handle the syncing as well.
The disk I'm using is a 2.5" external USB drive, in this article it's recognized as /dev/sdc by my computer. It has one partition that spans the entire drive: /dev/sdc1. This partition will be used to synchronize files to.
System info
- Debian Wheezy 64 bit
- udev version 175-7
Find out disk info
Plug in the external disk you will use. Then run udevadm info --query=all --name=/dev/sdc1 to get the list of device properties. Replace /dev/sdc1 with the name of the partition that you will use.
P: /devices/pci0000:00/0000:00:1d.0/usb4/4-1/4-1.2/4-1.2:1.0/host9/target9:0:0/9:0:0:0/block/sdc/sdc1
N: sdc1
S: disk/by-id/ata-WDC_WD2500BMVS-11F9S0_WD-WXH908713364-part1
S: disk/by-id/scsi-SWD_2500BMV_ExternaWD-WXH908713364-part1
S: disk/by-id/wwn-0x50014ee202191538-part1
S: disk/by-label/backupDisk
S: disk/by-path/pci-0000:00:1d.0-usb-0:1.2:1.0-scsi-0:0:0:0-part1
S: disk/by-uuid/94b94b63-4ec6-4e0c-a6f1-00fa03f00144
E: CUSTOM_RULE=1
E: DEVLINKS=/dev/disk/by-id/ata-WDC_WD2500BMVS-11F9S0_WD-WXH908713364-part1 /dev/disk/by-id/scsi-SWD_2500BMV_ExternaWD-WXH908713364-part1 /dev/disk/by-id/wwn-0x50014ee202191538-part1 /dev/disk/by-label/backupDisk /dev/disk/by-path/pci-0000:00:1d.0-usb-0:1.2:1.0-scsi-0:0:0:0-part1 /dev/disk/by-uuid/94b94b63-4ec6-4e0c-a6f1-00fa03f00144
E: DEVNAME=/dev/sdc1
E: DEVPATH=/devices/pci0000:00/0000:00:1d.0/usb4/4-1/4-1.2/4-1.2:1.0/host9/target9:0:0/9:0:0:0/block/sdc/sdc1
E: DEVTYPE=partition
E: ID_ATA=1
E: ID_ATA_DOWNLOAD_MICROCODE=1
E: ID_ATA_FEATURE_SET_AAM=1
E: ID_ATA_FEATURE_SET_AAM_CURRENT_VALUE=254
E: ID_ATA_FEATURE_SET_AAM_ENABLED=1
E: ID_ATA_FEATURE_SET_AAM_VENDOR_RECOMMENDED_VALUE=128
E: ID_ATA_FEATURE_SET_APM=1
E: ID_ATA_FEATURE_SET_APM_CURRENT_VALUE=128
E: ID_ATA_FEATURE_SET_APM_ENABLED=1
E: ID_ATA_FEATURE_SET_HPA=1
E: ID_ATA_FEATURE_SET_HPA_ENABLED=1
E: ID_ATA_FEATURE_SET_PM=1
E: ID_ATA_FEATURE_SET_PM_ENABLED=1
E: ID_ATA_FEATURE_SET_SECURITY=1
E: ID_ATA_FEATURE_SET_SECURITY_ENABLED=0
E: ID_ATA_FEATURE_SET_SECURITY_ENHANCED_ERASE_UNIT_MIN=96
E: ID_ATA_FEATURE_SET_SECURITY_ERASE_UNIT_MIN=96
E: ID_ATA_FEATURE_SET_SMART=1
E: ID_ATA_FEATURE_SET_SMART_ENABLED=1
E: ID_ATA_ROTATION_RATE_RPM=5400
E: ID_ATA_SATA=1
E: ID_ATA_SATA_SIGNAL_RATE_GEN1=1
E: ID_ATA_WRITE_CACHE=1
E: ID_ATA_WRITE_CACHE_ENABLED=1
E: ID_BUS=ata
E: ID_FS_LABEL=backupDisk
E: ID_FS_LABEL_ENC=backupDisk
E: ID_FS_TYPE=ext3
E: ID_FS_USAGE=filesystem
E: ID_FS_UUID=94b94b63-4ec6-4e0c-a6f1-00fa03f00144
E: ID_FS_UUID_ENC=94b94b63-4ec6-4e0c-a6f1-00fa03f00144
E: ID_FS_VERSION=1.0
E: ID_MODEL=WDC_WD2500BMVS-11F9S0
E: ID_MODEL_ENC=WDC\x20WD2500BMVS-11F9S0\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20
E: ID_PART_ENTRY_DISK=8:32
E: ID_PART_ENTRY_NUMBER=1
E: ID_PART_ENTRY_OFFSET=63
E: ID_PART_ENTRY_SCHEME=dos
E: ID_PART_ENTRY_SIZE=488392002
E: ID_PART_ENTRY_TYPE=0x83
E: ID_PART_TABLE_TYPE=dos
E: ID_PATH=pci-0000:00:1d.0-usb-0:1.2:1.0-scsi-0:0:0:0
E: ID_PATH_TAG=pci-0000_00_1d_0-usb-0_1_2_1_0-scsi-0_0_0_0
E: ID_REVISION=01.01A11
E: ID_SCSI_COMPAT=SWD_2500BMV_ExternaWD-WXH908713364
E: ID_SERIAL=WDC_WD2500BMVS-11F9S0_WD-WXH908713364
E: ID_SERIAL_SHORT=WD-WXH908713364
E: ID_TYPE=disk
E: ID_WWN=0x50014ee202191538
E: ID_WWN_WITH_EXTENSION=0x50014ee202191538
E: MAJOR=8
E: MINOR=33
E: SUBSYSTEM=block
E: UDEV_LOG=3
E: UDISKS_DISABLE_POLLING=1
E: UDISKS_PARTITION=1
E: UDISKS_PARTITION_ALIGNMENT_OFFSET=0
E: UDISKS_PARTITION_NUMBER=1
E: UDISKS_PARTITION_OFFSET=32256
E: UDISKS_PARTITION_SCHEME=mbr
E: UDISKS_PARTITION_SIZE=250056705024
E: UDISKS_PARTITION_SLAVE=/sys/devices/pci0000:00/0000:00:1d.0/usb4/4-1/4-1.2/4-1.2:1.0/host9/target9:0:0/9:0:0:0/block/sdc
E: UDISKS_PARTITION_TYPE=0x83
E: UDISKS_PRESENTATION_HIDE=1
E: UDISKS_PRESENTATION_NOPOLICY=1
E: USEC_INITIALIZED=1769647466311
Create udev rules
Create a new file in /etc/udev/rules.d and make sure the extension is .rules, e.g. /etc/udev/rules.d/99-diskSync.rules. The file will contain a rule to match the correct partition on the inserted disk. This rule will be taken from the udevadm output above.
My /etc/udev/rules.d/99-diskSync.rules looks like this:
SUBSYSTEM=="block", ENV{ID_SERIAL}=="WDC_WD2500BMVS-11F9S0_WD-WXH908713364", ENV{UDISKS_DISABLE_POLLING}="1", ENV{UDISKS_PRESENTATION_HIDE}="1", ENV{CUSTOM_RULE}="1", ENV{UDISKS_PRESENTATION_NOPOLICY}="1"
ACTION=="add", SUBSYSTEM=="block", ENV{ID_SERIAL}=="WDC_WD2500BMVS-11F9S0_WD-WXH908713364", ENV{ID_FS_LABEL}=="backupDisk", ENV{UDISKS_PRESENTATION_NOPOLICY}="1", RUN="/usr/local/sbin/dirSync.sh -d /dev/%k -m /media/%E{ID_FS_LABEL} -f -M tristan -s /var/lib/backuppc/ -t /backuppc/"
Several important things to note:
- The attributes I'm using to match my disk are very specific. If I simply used the serial number for the hard drive, the rule would match and the script would be executed. But it would be executed more than once, because the match is not specific enough: it matches
/dev/sdcand/dev/sdc1and possibly a number of other devices and the command specified byRUN=will be run for each match! RUN=overrides all otherRUNs from other matching rules. Before I created this rule, my external disk would get automatically mounted when I inserted it. I don't want that, I will have my script handle the (u)mounting.RUN="/usr/local/sbin/dirSync.sh -d /dev/%k -m /media/%E{ID_FS_LABEL} -f -M -s /sourceDir/ -t /targetDir/is run and is passed two udev fields,%k(e.g. "sdc1") and%E{ID_FS_LABEL}("backupDisk")
dirSync.sh
In the udev rule above, a command is called to perform the actual synchronization of the directory to the external disk. I've written the script dirSync.sh for that. It's available from my Bitbucket account: dirSync.sh @ Bitbuck.
Download the script to /usr/local/sbin/ and make sure it's executable.
Restart udev
Reload the udev rules with the command udevadm control --reload-rules.
Test
Plug in the device and let udev do the rest. If you're using my dirSync.sh, you can follow what's happening in the appropriate /tmp/dirSync.out file.