Avoid persistent overlay consumption
- Use a persistent home.img file system to mount on the /home folder (discussed on main page, LiveOS image#Home filesystem).
- This is a very effective method to avoid consumption and will also make the user files more available for sharing and backup purposes.
- Mount more folders onto temporary, in-memory filesystems (like /var/cache/yum, /var/tmp, & /tmp are now).
- /var/lib/NetworkManager (holds a timestamps file that is deleted and refreshed quite often, every 5 minutes)
- /var/log/audit (holds the SELinux audit.log that records a great many file accesses.)
- /var/spool/abrt (holds often large, error reports and core dumps). Users could be advised to act on any abrt reports in the current session or copy the reports to other permanent storage, such as in /home/ or external storage.
- there may be other good candidates...
Merge overlay into new image
A new root filesystem image can be constructed by using some Device-mapper tools.
If one has sufficient free disk space available, typically on an attached hard drive, one can copy (and uncompress) the current filesystem to a working folder. (This may require, for example, over 4.0 GiB of free space for Fedora 24 Live Workstation.)
Device-mapper's mirror target allows one to create a 'mirror' image of the LiveOS root filesystem (the snapshot based on the SquashFS and overlay device). The mirror image can be then be recompressed, and if one has an additional 1.5 GiB or more of free space (depending on how much software or other root filesystem files have been added) on your LiveOS device filesystem (the USB/SD card filesystem), one can delete the old SquashFS image and replace it with the recompressed version.
The snapshot overlay can then be reset before rebooting the LiveOS device.
The following Bash script demonstrates the process, where the $1 parameter is a mount point directory for a disk partition with sufficient storage capacity (a LiveOS folder will be created there for holding the mirrored filesystem), and $2 is the LiveOS device node name (such as, /run/initramfs/livedev, for the currently booted LiveOS image, or /dev/sdc1, for example, for an attached LiveOS device). Options xtrace and verbose have been set to aid debugging.
#!/bin/bash -xv # # Merge a LiveOS snapshot overlay into a new root filesystem, recompress it # into a SquashFS image (if the source was so packaged), replace the source # with the refresh, and reset the overlay. # # This program is free software; you can redistribute it and/or modify # it under the terms of the GNU General Public License as published by # the Free Software Foundation; version 2 of the License. # # This program is distributed in the hope that it will be useful, # but WITHOUT ANY WARRANTY; without even the implied warranty of # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the # GNU Library General Public License for more details. # # You should have received a copy of the GNU General Public License # along with this program; if not, write to the Free Software # Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. oldLC=$LC_NUMERIC LC_NUMERIC="en_US.UTF-8" export PATH=/usr/sbin:$PATH export \ PS4='+(${SHLVL}:${LINENO}:${BASH_SOURCE}:${EUID}): ${FUNCNAME[0]:+${FUNCNAME[0]}(): }' set -o errexit set -o pipefail t0=$(date +%s) cleanup () { umount -l $SRCMNT rmdir $SRCMNT dt=$(($(date +%s)-t0)) h=$((dt/3600)) m=$((dt%3600/60)) s=$((dt%60)) printf '\nTotal time elapsed: %02d:%02d:%02d hh:mm:ss\n' $h $m $s [[ $1 == 0 ]] && exit 0 || exit 1 } if [[ ! -f /usr/sbin/mksquashfs ]]; then echo "Please install squashfs-tools (yum install squashfs-tools)"; exit fi TMPDIR=$1 [[ ! -d $TMPDIR/LiveOS ]] && mkdir $TMPDIR/LiveOS 2>/dev/null # Mount the source device and SquashFS. mkdir -p /run/media #Doesn't exist in fedora 20 livecd SRCMNT=$(mktemp -d /run/media/XXXXXX) mount $2 $SRCMNT if [[ -e $SRCMNT/LiveOS/squashfs.img ]]; then SQUASHMNT=$(mktemp -d /run/media/XXXXXX) mount $SRCMNT/LiveOS/squashfs.img $SQUASHMNT --read-only ORIGFS=$SQUASHMNT/LiveOS/ext3fs.img [[ ! -f $ORIGFS ]] && ORIGFS=$SQUASHMNT/LiveOS/rootfs.img else ORIGFS=$SRCMNT/LiveOS/ext3fs.img [[ ! -f $ORIGFS ]] && ORIGFS=$SRCMNT/LiveOS/rootfs.img fi OVERLAY=/LiveOS/$(basename $SRCMNT/LiveOS/overlay-*) if [[ -f $SRCMNT$OVERLAY ]]; then OVDEV=$(losetup -f --show $SRCMNT$OVERLAY --read-only) else printf '\n No persistent overlay for the filesystem was found. Exiting...\n' cleanup 1 fi # >= Fedora 17 LiveOSMNT=/run/initramfs/live # < Fedora 17 [[ -d /mnt/live/LiveOS ]] && LiveOSMNT=/mnt/live # If we are processing a booted LiveOS device's root filesystem, then if [[ $(mountpoint -x $2) == $(mountpoint -dq $LiveOSMNT) ]]; then # Remove live-osimg-min; free its loop devices. if [[ -e $SRCMNT/LiveOS/osmin.img ]]; then dmsetup remove live-osimg-min || : losetup -d /dev/loop1 || : losetup -d /dev/loop0 || : fi else LiveOSMNT='' fi # Remove expiring osmin.img rm $SRCMNT/LiveOS/osmin.img || : # Prepare temporary devices for the Device-mapper mirror target. FSTYPE=$(blkid -s TYPE -o value $ORIGFS || :) FSLABEL=$(blkid -s LABEL -o value $ORIGFS || :) stinfo=($(stat -c '%B %s %o' $ORIGFS || :)) BLOCKSZ=${stinfo[0]} BLOCKS=$((${stinfo[1]}/$BLOCKSZ)) IOBLKSZ=${stinfo[2]} NEWFS=$TMPDIR/LiveOS/rootfs.img dd if=/dev/null of=$NEWFS count=1 bs=$BLOCKSZ seek=$BLOCKS mkfs.$FSTYPE -F -L $FSLABEL -m 1 -b $IOBLKSZ $NEWFS tune2fs -c0 -i0 -Odir_index -ouser_xattr,acl $NEWFS NEWFSDEV=$(losetup -f --show $NEWFS) roORIGFSDEV=$(losetup -f --show $ORIGFS --read-only) table="0 $BLOCKS snapshot $roORIGFSDEV $OVDEV P 8" dmsetup create ori --readonly --table "$table" # Invoke mirror target device. table="0 $BLOCKS mirror core 2 32 sync 2 /dev/mapper/ori 0 $NEWFSDEV 0" dmsetup create mir --table "$table" set +xv # Wait for mirror completion. while state=$(dmsetup status mir) state=${state#*mirror 2 * * } alloc=${state%/*} size=${state#*/} size=${size%% *} [[ $alloc != $size ]]; do percent=$(dc <<< "8k 10 0.05 100 $alloc $size /*+*p") percent=$(dc <<< "1k $percent 10 /p") printf '\r Mirroring %5.1f %% complete. ' $percent printf '\b|' sleep 0.5 printf '\b/' sleep 0.5 printf '\b-' sleep 0.5 printf '\b\' sleep 0.5 done printf '\r Mirroring 100 %% complete. \n' set -xv # Check the new filesystem. e2fsck -f -y $NEWFS || e2fsck -f -y $NEWFS # Clean up. dmsetup remove mir ori sync dt=$(($(date +%s)-t0)) h=$((dt/3600)) m=$((dt%3600/60)) s=$((dt%60)) printf '\nTime elapsed: %02d:%02d:%02d hh:mm:ss\n' $h $m $s # Replace SquashFS or uncompressed root filesystem image. if [[ -e $SRCMNT/LiveOS/squashfs.img ]]; then umount -l $SQUASHMNT rm $SRCMNT/LiveOS/squashfs.img mksquashfs $TMPDIR/LiveOS $SRCMNT/LiveOS/squashfs.img -comp xz -keep-as-directory else if [[ -x /usr/bin/rsync ]]; then rsync --inplace --progress $NEWFS $SRCMNT/LiveOS else cp $NEWFS $SRCMNT/LiveOS fi fi # Clean up. losetup -d $OVDEV $NEWFSDEV $roORIGFSDEV OVDEV=$(losetup -f --show $SRCMNT$OVERLAY) # Reset overlay. dd if=/dev/zero of=$OVDEV bs=64k count=1 conv=notrunc,fsync # If we are processing a booted LiveOS device's root filesystem, then if [[ -n $LiveOSMNT ]]; then # Try to unmount the TMPDIR. mountpoint $TMPDIR && umount -l $TMPDIR || : shutdown -r +1 'The system will reboot in 1 minute.' else sleep 1 losetup -d $OVDEV fi cleanup 0
Note: If the above script is invoked on a currently booted LiveOS root filesystem, the system will be scheduled for a reboot one minute after the script completes.
The Device-mapper snapshot-merge target also allows one to merge changes in a persistent snapshot into the original filesystem (See notes from Andrew Gilmore).
Merge overlay with snapshot-merge |
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#!/bin/bash t0=$(date +%s) # Prepare working directory. TMPDIR=$1 mkdir $TMPDIR/LiveOS 2>/dev/null # Mount source device, SquashFS, if needed. SRCMNT=$(mktemp -d /media/XXXXXX) mount $2 $SRCMNT if [[ -e $SRCMNT/LiveOS/squashfs.img ]]; then SQUASHMNT=$(mktemp -d /media/XXXXXX) mount $SRCMNT/LiveOS/squashfs.img $SQUASHMNT --read-only ORIGFS=$SQUASHMNT/LiveOS/ext3fs.img else ORIGFS=$SRCMNT/LiveOS/ext3fs.img fi NEWFS=$TMPDIR/LiveOS/ext3fs.img printf '\nCopying original root filesystem.\n' if [[ -x /usr/bin/rsync ]]; then rsync --inplace --progress $ORIGFS $NEWFS else cp $ORIGFS $NEWFS fi # Prepare temporary devices for Device-mapper snapshot-merge. BLOCKS=$(stat -c '%b' $ORIGFS || :) NEWFSDEV=$(losetup -f --show $NEWFS) OVDEV=$(losetup -f --show $SRCMNT/LiveOS/overlay-*) # Invoke snapshot-merge target device. dmsetup create merge <<< "0 $BLOCKS snapshot-merge $NEWFSDEV $OVDEV P 8" # Wait for merge completion. while state=$(dmsetup status merge) state=${state#*snapshot-merge } meta=${state#* } alloc=${state%/*} [[ $alloc != $meta ]]; do printf '/' sleep 0.5 printf '\b-' sleep 0.5 printf '\b\' sleep 0.5 printf '\b|' sleep 0.5 done printf '\n' # Clean up from merge. dmsetup remove merge sync dt=$(($(date +%s)-t0)) h=$((dt/3600)) m=$((dt%3600/60)) s=$((dt%60)) printf '\nTime elapsed: %02d:%02d:%02d hh:mm:ss\n' $h $m $s # Replace original image if [[ -e $SRCMNT/LiveOS/squashfs.img ]]; then umount $SQUASHMNT rmdir $SQUASHMNT rm $SRCMNT/LiveOS/squashfs.img mksquashfs $TMPDIR/LiveOS $SRCMNT/LiveOS/squashfs.img -comp xz -keep-as-directory else if [[ -x /usr/bin/rsync ]]; then rsync --inplace --progress $NEWFS $SRCMNT/LiveOS else cp $NEWFS $SRCMNT/LiveOS fi fi # Reset overlay. dd if=/dev/zero of=$OVDEV bs=64k count=1 conv=notrunc,fsync # Clean up. sleep 2 losetup -d $OVDEV $NEWFSDEV sleep 2 umount $SRCMNT rmdir $SRCMNT LC_NUMERIC=$oldLC dt=$(($(date +%s)-t0)) h=$((dt/3600)) m=$((dt%3600/60)) s=$((dt%60)) printf '\nTotal time elapsed: %02d:%02d:%02d hh:mm:ss\n' $h $m $s |
The mirror method copies and merges in one pass, while the snapshot-merge method copies the original filesystem first and then merges in the changes. I've found the mirror method to be about 15% faster.
editliveos.py is a Python script that performs overlay merging and, optionally, other Live OS editing. It should be run from a directory containing these supporting files.
Overlay recovery
If one 'exhausts' the limited storage capacity of a LiveOS overlay, Device-mapper will mark the filesystem as 'Invalid', as shown by the dmsetup status command executed in Terminal or a console (if you haven't crashed):
# dmsetup status live-osimg-min: 0 8388608 snapshot 2464/2464 24 live-rw: 0 8388608 snapshot Invalid
The invalid bit is 00 at byte 5 of the overlay. You might try to recover the overlay by switching it to 01 with the following command line:
# echo $'\x01' | dd of=/path/to/overlay-file bs=1 count=1 seek=4 conv=notrunc
where /path/to/overlay may be /mnt/live/LiveOS/overlay-devicename-discUUID or
/media/devicename/LiveOS/overlay-devicename-discUUID for an attached device.
Follow this by registering the LiveOS image with Device-mapper:
# mount /media/devicename/LiveOS/squashfs.img /mnt/some_mountpoint # losetup /dev/loop1 /mnt/some_mountpoint/LiveOS/ext3fs.img -r # losetup /dev/loop2 /media/devicename/LiveOS/overlay-devicename-discUUID # dmsetup create devicename --table "0 8388608 snapshot 7:1 7:2 P 8"
- devicename in the last line may be any string.
- loop1 and loop2 (and the corresponding 7:1 7:2) may be any free loop devices; just substitute the appropriate numbers.
- 8388608 is the size of the ext3fs.img file in 512 byte units. This can be read by the following command:
# blockdev -q --getsz /dev/loop1
Execute
# dmsetup status
to check the the virtual filesystem has been configured.
Then try to repair any damage with the following command:
# e2fsck -f -y /dev/mapper/devicename
where devicename is the string you used in the dmsetup create command.
Run a second check,
# e2fsck -p /dev/mapper/devicename
to verify if the filesystem could be repaired. At this point you will want to enlarge the overlay, or backup or rebuild the image.
Remove the virtual filesystem registration,
# dmsetup remove devicename
Determine the size of the overlay file:
# blockdev -q --getsz /dev/loop2 # losetup -d /dev/loop2 # losetup -d /dev/loop1 # dd if=/dev/zero of=/path/to/overlay-file seek=overlay_size count=size_increase
where overlay_size and size_increase are now 512 byte units.
Once you have a working filesystem, you should proceed to merge your overlay into the original filesystem as described above.