Backing Up Filesystems on M-Series and T-Series Routers

Problem

You are preparing to load a different release of the JUNOS software or reload the current release and you want to save the files that are already on the router.

Solution

On M-series and T-series routers, use the following command to back up the files in the router's filesystems:

aviva@router1> request system snapshot

Discussion

Before you install any JUNOS software, either upgrading, downgrading, or reinstalling the current software version, you should always back up the files in the router's filesystem. This operation is sometimes called taking a snapshot of the software. The request system snapshot command copies the files and filesystems from the current running active partitions to standby partitions. Specifically, it copies the / (root) filesystem to /altroot, and the /config filesystem to /altconfig. You see information about the copying as the command is running:

aviva@router1> request system snapshot Copying '/' to '/altroot' .. (this may take a few minutes) Copying '/config' to '/altconfig' .. (this may take a few minutes) The following filesystems were archived: / /config

You can take a snapshot of the software at any time, but you should always do so before installing a new JUNOS software version so that you can recover to a known, stable environment in case something goes wrong when you load the software. You should also always run it after you have successfully loaded a new version of the software.

Why do you need to back up the JUNOS filesystems? One seasoned administrator has said that the less you know about the JUNOS filesystems, the more sane you will bebut still, you have to know at least a little bit. Routers have two internal storage areas, the flash drive (by default, the primary boot device) and the hard disk (the secondary boot device). A copy of the JUNOS software is stored in both. The flash drive has two filesystems (or partitions): /config, which contains the active and most recent backup configurations, the rescue configuration, and software licenses, and /, which contains the JUNOS software (everything installed by the jinstall or jbundle command), the router's SSH keys, and a few other files generated from the configuration. The hard disk has one filesystem, /var, which is a large partition that contains system logfiles, diagnostic dump files, archived configuration files, and user home directories.(Also on the hard disk are the /altroot and /altconfig partitions, which contain a copy of the JUNOS software and related files and a swap partition.) When booting from the flash drive, the router uses the software and files on the flash drive. If the boot fails, it automatically tries the software and files on the hard disk. For the boot failover process to work, you must have already created a snapshot from a working version of the software.

There is one additional filesystem on the router, /tmp, which is a RAM disk (a memory filesystem).

To verify that the snapshot was successful, you might want to list the contents of the filesystems (with the file list command). However, the /altroot and /altconfig filesystems are not mounted, so they are not visible even though the underlying directories are still present:

aviva@router1> show system storage Filesystem Size Used Avail Capacity Mounted on /dev/ ad0s1a 77M 39M 32M 55% /devfs 16K 16K 0B 100% /dev/ /dev/vn0 13M 13M 0B 100% /packages/mnt/jbase /dev/vn1 37M 37M 0B 100% /packages/mnt/jkernel-7.4R1.7 /dev/vn2 12M 12M 0B 100% /packages/mnt/jpfe-M40-7.4R1.7 /dev/vn3 2.3M 2.3M 0B 100% /packages/mnt/jdocs-7.4R1.7 /dev/vn4 14M 14M 0B 100% /packages/mnt/jroute-7.4R1.7 /dev/vn5 5.1M 5.1M 0B 100% /packages/mnt/jcrypto-7.4R1.7 /dev/ad0s1e 12M 16K 11M 0% /config procfs 4.0K 4.0K 0B 100% /proc /dev/ ad1s1f 9.4G 1.2G 7.4G 14% /var

How do you know from the output of this command which partition is where? /dev/ad0s1a refers to a portion of a disk. It is drive ad0 (the storage device) slice 1 (the first "slice," and there's generally just one slice), partition a (which is the first partition on a disk and always refers to the root partition). Similarly, /dev/ad1s1f refers to drive ad1, slice 1, partition f.

On most M-and T-series routers, ad0 is the flash disk. In the case of router1, an M20 router that has an RE-2.0, ad0 is the flash disk and ad1 is the hard disk:

aviva@router1> show chassis hardware detail Hardware inventory: Item Version Part number Serial number Description Chassis 25708 M20 Backplane REV 03 710-002334 BB9738 M20 Backplane Power Supply A REV 06 740-001465 005234 AC Power Supply Display REV 04 710-001519 BA4681 M20 FPM Board Routing Engine 0 REV 06 740-003239 1000224893 RE-2.0 Routing Engine 0 58000007348d9a01 RE-2.0 ad0 91 MB SanDisk SDCFB-96 i3238140903 Compact Flash ad1 11513 MB IBM-DARA-212000 AH0AHGN1017 Hard Disk Routing Engine 1 REV 06 740-003239 9000022146 RE-2.0 Routing Engine 1 d800000734745701 RE-2.0 ad0 91 MB SanDisk SDCFB-96 ggbsc410020 Compact Flash ad1 8063 MB TOSHIBA MK2016GAP Y0T39909T Hard Disk …

The output of this command also shows the manufacturer of the disks.

Use the show system storage command to find out the drive names:

aviva@router1> show system storage Filesystem Size Used Avail Capacity Mounted on /dev/ad0s1a 77M 40M 31M 56% / devfs 16K 16K 0B 100% /dev/ /dev/vn0 13M 13M 0B 100% /packages/mnt/jbase /dev/vn1 37M 37M 0B 100% /packages/mnt/jkernel- 7.3-20050504.0 /dev/vn2 12M 12M 0B 100% /packages/mnt/jpfe-M40- 7.3-20050504.0 /dev/vn3 2.3M 2.3M 0B 100% /packages/mnt/jdocs-7. 3-20050504.0 /dev/vn4 14M 14M 0B 100% /packages/mnt/jroute-7. 3-20050504.0 /dev/vn5 5.1M 5.1M 0B 100% /packages/mnt/jcrypto- 7.3-20050504.0 mfs:102 1.5G 12K 1.4G 0% /tmp /dev/ad0s1e 12M 24K 11M 0% /config procfs 4.0K 4.0K 0B 100% /proc /dev/ad1s1f 9.4G 2.4G 6.2G 28% /var

You see that /dev/ad0s1a is mounted at /, and you know that's the flash disk. /config is also on ad0 (the flash disk again) but on a different partition, and /var is on ad1 (the hard disk). The /dev/vn0 devices refer to the software installed on the router. All these partitions are stored on / (and /altroot).

The show system storage command output is cluttered and contains more information than you normally care about. You can shorten by filtering out the installed software devices:

aviva@router1> show system storage | except /dev/vn Filesystem Size Used Avail Capacity Mounted on /dev/ad0s1a 77M 39M 32M 55% / devfs 16K 16K 0B 100% /dev/ mfs:102 1.5G 8.0K 1.4G 0% /tmp /dev/ad0s1e 12M 16K 11M 0% /config procfs 4.0K 4.0K 0B 100% /proc /dev/ad1s1f 9.4G 1013M 7.6G 11% /var

or even more:

aviva@router1> show system storage | match ad /dev/ad0s1a 77M 39M 32M 55% / /dev/ad0s1e 12M 16K 11M 0% /config /dev/ad1s1f 9.4G 1013M 7.6G 11% /var

If the router boots from the hard disk or if you manually reboot from the hard disk (take a fresh snapshot first, though), you'll notice that ad0 is still the flash disk and ad1 is still the hard disk, but the root filesystem is now on the hard disk because you're running on alternate media:

aviva@router1> request system reboot media disk aviva@router1> show system storage Filesystem Size Used Avail Capacity Mounted on /dev/ad1s1a 107M 37M 61M 38% / . . . mfs:172 1.9G 4.0K 1.8G 0% /tmp /dev/ad1s1e 12M 21K 11M 0% /config procfs 4.0K 4.0K 0B 100% /proc /dev/ad1s1f 25G 3.5G 19G 15% /var

The request system reboot media disk command takes a fairly long time to complete, and you need to log back in to the router when it completes.

See Also

Recipe 1.20