create_swap do not fallback to dd when fallocate fails

[Evaggelos Balaskas]

Name : cloud-init
Version : 20.2-1

Code in questioning: cloudinit/config/cc_mounts.py

        try:
            create_swap(fname, size, "fallocate")
        except util.ProcessExecutionError as e:
            LOG.warning(errmsg, fname, size, "dd", e)
            LOG.warning("Will attempt with dd.")
            create_swap(fname, size, "dd")

as there is a kernel bug in latest's linux versions, fallocate creates swap images with holes.
The workaround is to move fallocate (make create_swap function to fail) so that cloud-init will fallback to dd.

Used bootcmd (or cloud-boothook) to rename (move) fallocate binary from my system but according the the logs, it didnt fallback to dd as it should. Probably the error was not ProcessExecutionError

Logs:

/var/log/cloud-init-output.log:2020-09-24 09:13:16,470 - cc_mounts.py[WARNING]: Failed to create swapfile '/swapfile' of size 2048MB via fallocate: Unexpected
 error while running command.
/var/log/cloud-init-output.log:Command: ['fallocate', '-l', '2048M', '/swapfile']
/var/log/cloud-init-output.log:Reason: [Errno 2] No such file or directory: b'fallocate'
/var/log/cloud-init-output.log:2020-09-24 09:13:16,479 - cc_mounts.py[WARNING]: failed to setup swap: [Errno 2] No such file or directory: '/swapfile'
/var/log/cloud-init-output.log:chmod: cannot access '/usr/bin/fallocate': No such file or directory
/var/log/cloud-init.log:2020-09-24 09:13:16,460 - cc_mounts.py[DEBUG]: Attempting to determine the real name of swap
/var/log/cloud-init.log:2020-09-24 09:13:16,460 - cc_mounts.py[DEBUG]: changed default device swap => None
/var/log/cloud-init.log:2020-09-24 09:13:16,460 - cc_mounts.py[DEBUG]: Ignoring nonexistent default named mount swap
/var/log/cloud-init.log:2020-09-24 09:13:16,461 - cc_mounts.py[DEBUG]: suggest 2048.0 MB swap for 1983.953125 MB memory with '9030.296875 MB' disk given max=2048.0 MB [max=2048.0 MB]'
/var/log/cloud-init.log:2020-09-24 09:13:16,461 - cc_mounts.py[DEBUG]: Creating swapfile in '/swapfile' on fstype 'ext4' using 'fallocate'
/var/log/cloud-init.log:2020-09-24 09:13:16,461 - util.py[DEBUG]: Running command ['fallocate', '-l', '2048M', '/swapfile'] with allowed return codes [0] (she
ll=False, capture=True)
/var/log/cloud-init.log:2020-09-24 09:13:16,470 - cc_mounts.py[WARNING]: Failed to create swapfile '/swapfile' of size 2048MB via fallocate: Unexpected error while running command.
/var/log/cloud-init.log:Command: ['fallocate', '-l', '2048M', '/swapfile']
/var/log/cloud-init.log:Reason: [Errno 2] No such file or directory: b'fallocate'
/var/log/cloud-init.log:2020-09-24 09:13:16,479 - util.py[DEBUG]: Attempting to remove /swapfile
/var/log/cloud-init.log:2020-09-24 09:13:16,479 - util.py[DEBUG]: Setting up swap file took 0.019 seconds
/var/log/cloud-init.log:2020-09-24 09:13:16,479 - cc_mounts.py[WARNING]: failed to setup swap: [Errno 2] No such file or directory: '/swapfile'

[Chad Smith (chad.smith)]

This bug is believed to be fixed in cloud-init in version 20.4. If this is still a problem for you, please make a comment and set the state back to New

Thank you.

[Evaggelos Balaskas (ebal)]

I can confirm via archlinux as 20.04 isnt yet in ubuntu

I consider this bug fixed and closed !

thanks

$ grep swap /var/log/cloud-init.log
2020-12-25 08:38:14,611 - cc_mounts.py[DEBUG]: Attempting to determine the real name of swap
2020-12-25 08:38:14,611 - cc_mounts.py[DEBUG]: changed default device swap => None
2020-12-25 08:38:14,611 - cc_mounts.py[DEBUG]: Ignoring nonexistent default named mount swap
2020-12-25 08:38:14,612 - cc_mounts.py[DEBUG]: suggest 2048.0 MB swap for 1983.93359375 MB memory with '9078.94921875 MB' disk given max=2048.0 MB [max=2048.0 MB]'
2020-12-25 08:38:14,612 - cc_mounts.py[DEBUG]: Creating swapfile in '/swapfile' on fstype 'ext4' using 'fallocate'
2020-12-25 08:38:14,612 - subp.py[DEBUG]: Running command ['fallocate', '-l', '2048M', '/swapfile'] with allowed return codes [0] (shell=False, capture=True)
2020-12-25 08:38:14,616 - cc_mounts.py[INFO]: Failed to create swapfile '/swapfile' of size 2048MB via fallocate: Unexpected error while running command.
Command: ['fallocate', '-l', '2048M', '/swapfile']
2020-12-25 08:38:14,616 - util.py[DEBUG]: Attempting to remove /swapfile
2020-12-25 08:38:14,616 - cc_mounts.py[INFO]: fallocate swap creation failed, will attempt with dd
2020-12-25 08:38:14,616 - cc_mounts.py[DEBUG]: Creating swapfile in '/swapfile' on fstype 'ext4' using 'dd'
2020-12-25 08:38:14,616 - subp.py[DEBUG]: Running command ['dd', 'if=/dev/zero', 'of=/swapfile', 'bs=1M', 'count=2048'] with allowed return codes [0] (shell=False, capture=True)
2020-12-25 08:38:34,284 - subp.py[DEBUG]: Running command ['mkswap', '/swapfile'] with allowed return codes [0] (shell=False, capture=True)
2020-12-25 08:38:42,346 - util.py[DEBUG]: Setting up swap file took 27.734 seconds
2020-12-25 08:38:42,350 - cc_mounts.py[DEBUG]: Changes to fstab: ['+ /swapfile none swap sw,comment=cloudconfig 0 0']
2020-12-25 08:38:42,350 - subp.py[DEBUG]: Running command ['swapon', '-a'] with allowed return codes [0] (shell=False, capture=True)
2020-12-25 08:38:42,387 - cc_mounts.py[DEBUG]: Activate mounts: PASS:swapon -a

$ pacman -Qi cloud-init
Name : cloud-init
Version : 20.4-1
Description : The standard for customising cloud instances
Architecture : any
URL : https://cloud-init.io
Licenses : GPL3

[James Falcon (falcojr)]

Tracked in Github Issues as https://github.com/canonical/cloud-init/issues/3790