4 ms·

Cache Directory Tagging Specification (2004)

21 points by networked 2y ago

Cyphase 2y ago
I think this is my favorite lesser known spec, for whatever reason. I smile whenever I run across a CACHEDIR.TAG.
- chubot 2y ago
  Which apps use it?
  - keybored 2y ago
    GNU tar has `--exclude-caches-all` which uses it. Also apparently some tool named “dar”.[1] There’s also 18 hits on Stackoverflow. [1] Via the link from another comment https://github.com/RsyncProject/rsync/issues/499 https://github.com/RsyncProject/rsync/issues/499
  - networked 2y ago
    BorgBackup and restic have the CLI option `--exclude-caches`. https://borgbackup.readthedocs.io/en/stable/usage/create.html https://borgbackup.readthedocs.io/en/stable/usage/create.htm... https://restic.readthedocs.io/en/stable/040_backup.html#excluding-files https://restic.readthedocs.io/en/stable/040_backup.html#excl...
Rygian 2y ago
Support in rsync seems to be lacking, unfortunately: https://github.com/RsyncProject/rsync/issues/499 https://github.com/RsyncProject/rsync/issues/499
keybored 2y ago
Good idea. > Case is important in the header signature, there can be no whitespace or other characters in the file before the 'S', Much as I dislike BOM... maybe a BOM could be permitted with “a run of Unicode whitespace is permitted before the `S`”. > The hex value in the signature happens to be the MD5 hash of the string ".IsCacheDirectory". This signature header is required to avoid the chance of an unrelated file named CACHEDIR.TAG being mistakenly interpreted as a cache directory tag by data management utilities, and (for example) causing valuable data not to be backed up. Nice use of a “magic string” for the format. But (for extra magic) could have just picked a UUID. Just any random one.
- theamk 2y ago
  This is Linux spec, which is UTF-8 based. BOM makes absolutely no sense in UTF-8 world. (Plus "a run of Unicode whitespace" is a very heavy-weight thing, as it requires full Unicode database and Unicode parsers. It is pretty likely that apps which might care about cachedir tag will not have this linked in by default.)
  - keybored 2y ago
    I’m so sorry.

21 points by networked 2y ago

Cyphase 2y ago

I think this is my favorite lesser known spec, for whatever reason. I smile whenever I run across a CACHEDIR.TAG.

chubot 2y ago
Which apps use it?
- keybored 2y ago
  GNU tar has `--exclude-caches-all` which uses it. Also apparently some tool named “dar”.[1] There’s also 18 hits on Stackoverflow. [1] Via the link from another comment https://github.com/RsyncProject/rsync/issues/499 https://github.com/RsyncProject/rsync/issues/499
- networked 2y ago
  BorgBackup and restic have the CLI option `--exclude-caches`. https://borgbackup.readthedocs.io/en/stable/usage/create.html https://borgbackup.readthedocs.io/en/stable/usage/create.htm... https://restic.readthedocs.io/en/stable/040_backup.html#excluding-files https://restic.readthedocs.io/en/stable/040_backup.html#excl...

Rygian 2y ago

Support in rsync seems to be lacking, unfortunately: https://github.com/RsyncProject/rsync/issues/499 https://github.com/RsyncProject/rsync/issues/499

keybored 2y ago

Good idea. > Case is important in the header signature, there can be no whitespace or other characters in the file before the 'S', Much as I dislike BOM... maybe a BOM could be permitted with “a run of Unicode whitespace is permitted before the `S`”. > The hex value in the signature happens to be the MD5 hash of the string ".IsCacheDirectory". This signature header is required to avoid the chance of an unrelated file named CACHEDIR.TAG being mistakenly interpreted as a cache directory tag by data management utilities, and (for example) causing valuable data not to be backed up. Nice use of a “magic string” for the format. But (for extra magic) could have just picked a UUID. Just any random one.

theamk 2y ago
This is Linux spec, which is UTF-8 based. BOM makes absolutely no sense in UTF-8 world. (Plus "a run of Unicode whitespace" is a very heavy-weight thing, as it requires full Unicode database and Unicode parsers. It is pretty likely that apps which might care about cachedir tag will not have this linked in by default.)
- keybored 2y ago
  I’m so sorry.