Config file truncated when low on disk space

[simon816]

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The bug

When the disk that Nextcloud is installed on is full (an admittedly unpredictable scenario), the config file is truncated. This happened during an update in my case.

Steps to reproduce

1. cat config/config.php, observe config values
2. Fill up disk space, e.g. dd if=/dev/zero of=file.dat bs=1024 count=10000000
3. Perform action that changes config file, e.g. occ maintenance:mode --on
4. cat config/config.php observe an empty file

Expected behaviour

Config file is not truncated when no disk space.

Actual behaviour

Config is left empty, Nextcloud believes it is no longer installed and wants a CAN_INSTALL file.

Server configuration

Operating system:
Ubuntu 18.04.5 LTS

Web server:
apache2 2.4.29-1ubuntu4.14

Database:
mariadb 10.1.44

PHP version:
PHP 7.2.24-0ubuntu0.18.04.6

Nextcloud version: (see Nextcloud admin page)
20.0.5

[szaimen]

Is this Issue still valid in NC21.0.2? If not, please close this issue. Thanks! :)

[ghost]

This issue has been automatically marked as stale because it has not had recent activity and seems to be missing some essential information. It will be closed if no further activity occurs. Thank you for your contributions.

[simon816]

Can confirm on NC 21.0.2.1

Created an Ubuntu 20.04 VM with Nextcloud installed and filled the disk:

[szaimen]

cc @nextcloud/server seems like this is still happening

[juliusknorr]

I think we should probably write the new content to a temp file next to the existing one and the do a rename as any other checks for available space might still lead to scenarios where the check passes but the write then fails if the disk runs out of space in the meantime.

[stefan123t]

What about the file permissions associated with the original config.php ?
Are facls carried over too ?
Would it be better to first append the necessary bytes (eg comment or newlines) to the file and later write the new contents once the file is large enough ?

[come-nc]

Fixed by #34009

[come-nc]

Fixed by #34009

Reverted #34137

[szaimen]

Hi @simon816 can you please check if #36691 fixes the issue for you? Thanks a lot! :)

[simon816]

Hi @szaimen, indeed it does, thanks. Of course there's a TOCTOU race condition there but I expect it's fine for the majority of cases.

[nursoda]

I see these messages in log for each web directory access in NC26beta3:

disk_free_space(): No such file or directory at …/lib/private/Files/Storage/Local.php#421

full nextcloud.log entry

{
  "reqId": "xucm63dW56R2nOpKqqUD",
  "level": 3,
  "time": "2023-02-15T14:59:17+01:00",
  "remoteAddr": "192.168.1.2",
  "user": "MYUSER",
  "app": "PHP",
  "method": "PROPFIND",
  "url": "/remote.php/dav/files/SOMEPATH",
  "message": "disk_free_space(): No such file or directory at /DATAFOLDER/lib/private/Files/Storage/Local.php#421",
  "userAgent": "Mozilla/5.0 (X11; Linux x86_64; rv:109.0) Gecko/20100101 Firefox/110.0",
  "version": "26.0.0.5",
  "data": {
    "app": "PHP"
  }
}

Is that related with this enhancement? This is not a race condition, this happens on each access and should be fixed.

[szaimen]

Is that related with this enhancement?

It is not included in nc26beta3 yet so unrelated.

[nursoda]

Found the issue – it's an older one, not 26 specific.