Ygtjki

I am working with a script that does system back up. One part of the script backs up /, /opt, and /usr/local. But isn't /opt and /usr/local under /? So why would the script back these up separately? I understand why /home is backed up separately since it's on a separate partition /dev/sda3. But /opt and /usr/local are both on same partition as root, /dev/sda2. Can someone explain why the root partition has multiple mount points and why filesystems that appear to be within a single file system are backed up separately?

Script snippet:

# these are on btrfs file systems so we must use tar
# /
# /opt
# /usr/local

TARFS() 
 if [ $ITER -ne 0 ]; then SETERR $ITER; fi # main pid SETERR is redundant
 if [ "$1" = "." ]; then NAME=root; else NAME=$1; fi
 LOG "Starting tarball backup of $NAME in BG - $ITER"
 tar cfz $NOW/$NAME.tgz 2>> $EFILE --one-file-system $1
 if [ $? -ne 0 -o -s $EFILE ]; then WARN tarballing $NAME;
 else LOG Completed tar of $NAME; fi
 if [ $ITER -ne 0 ]; then CLEANERR; fi


if [ $PARM1 -eq 0 ]; then # level 0 - weekly stuff
 sleep 10; ITERATE
 TARFS . &
 sleep 10; ITERATE
 (cd usr; TARFS local) &
 sleep 10; ITERATE
 TARFS opt # not in BG due to DB ops coming
fi 

Output from df -hT:

Filesystem Type Size Used Avail Use% Mounted on
/dev/sda2 btrfs 41G 16G 25G 39% /
devtmpfs devtmpfs 64G 4.0K 64G 1% /dev
tmpfs tmpfs 64G 76K 64G 1% /dev/shm
tmpfs tmpfs 64G 67M 64G 1% /run
tmpfs tmpfs 64G 0 64G 0% /sys/fs/cgroup
/dev/sda2 btrfs 41G 16G 25G 39% /.snapshots
/dev/sda2 btrfs 41G 16G 25G 39% /var/spool
/dev/sda2 btrfs 41G 16G 25G 39% /var/crash
/dev/sda2 btrfs 41G 16G 25G 39% /var/tmp
/dev/sda2 btrfs 41G 16G 25G 39% /usr/local
/dev/sda2 btrfs 41G 16G 25G 39% /var/opt
/dev/sda2 btrfs 41G 16G 25G 39% /var/lib/pgsql
/dev/sda2 btrfs 41G 16G 25G 39% /var/lib/named
/dev/sda2 btrfs 41G 16G 25G 39% /var/lib/mailman
/dev/sda2 btrfs 41G 16G 25G 39% /tmp
/dev/sda2 btrfs 41G 16G 25G 39% /srv
/dev/sda2 btrfs 41G 16G 25G 39% /opt
/dev/sda2 btrfs 41G 16G 25G 39% /boot/grub2/x86_64-efi
/dev/sda2 btrfs 41G 16G 25G 39% /boot/grub2/i386-pc
/dev/sda2 btrfs 41G 16G 25G 39% /var/log
/dev/sde1 xfs 1.0T 125G 899G 13% /Dbbkup
/dev/sdd1 xfs 1.0T 21G 1003G 3% /C
/dev/sda3 xfs 982G 1.3G 981G 1% /home
/dev/sdb1 xfs 1.0T 522G 502G 51% /D
/dev/sdc1 xfs 1.0T 325G 699G 32% /E

Output from lsblk:

NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
fd0 2:0 1 4K 0 disk
sda 8:0 0 1T 0 disk
ââsda1 8:1 0 2G 0 part [SWAP]
ââsda2 8:2 0 40G 0 part /
ââsda3 8:3 0 982G 0 part /home
sdb 8:16 0 1T 0 disk
ââsdb1 8:17 0 1024G 0 part /D
sdc 8:32 0 1T 0 disk
ââsdc1 8:33 0 1024G 0 part /E
sdd 8:48 0 1T 0 disk
ââsdd1 8:49 0 1024G 0 part /C
sde 8:64 0 1T 0 disk
ââsde1 8:65 0 1024G 0 part /Dbbkup
sr0 11:0 1 1024M 0 rom

/opt and /usr/local/ are subvolumes in a btrfs filesystem (look for subvol= in /etc/fstab to confirm). Subvolumes are similar to partitions in that Tar treats btrfs subvolumes as seperate mount points and will skip them if --one-file-system option is set. This is why (1) the sda2 partition appears as multiple mount points, and (2) when backing up /, /opt and /usr/local/ are skipped and must be backed up separately.