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How to share a folder in Linux? (mander.xyz)

submitted 1 week ago by ranzispa@mander.xyz to c/sysadmin@lemmy.world

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I work on an HPC and often I have to share files with other users. The most approachable solution is to have an external cloud storage and recline back and forth. However there's some projects that are quite heavy (several TB) and that is unfeasible. We do not have a shared group. The following is the only solution I found which is not to just set al permissions to 777, and I still don't like it.

Create a directory and set ACL to give access to the selected users. This works fine if the users create new files in there, but it does not work if they copy from somewhere else as default umask is 022. Thus the only appropriate solution is to change default umask to 002, which however affects file creation system wide. The alternative is to change permissions every time you copy something, but you all know very well that is not going to happen.

Does it really have to be such a pain in the ass?

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[–] ranzispa@mander.xyz 1 points 1 week ago* (last edited 1 week ago) (1 children)

Default user entries are in there and do work, however when copying existing files those get masked with the existing group permissions. As such, the only solution I found is to have everyone set their umask to 002 as otherwise we would not get write access to files which are copied and not created in place.

[–] CallMeAl@piefed.zip 2 points 1 week ago (1 children)

Ah, I see. Well its ugly, but you could inotify to trigger a tiny script to update the perms when files are added or copied to the share dir.

[–] ranzispa@mander.xyz 0 points 1 week ago (1 children)

That is a possibility, but how would the setup look like? Only the owner can update the permissions. This would mean that all users need an inotify daemon on that folder for whenever they copy something in there. Not to mention, this is an HPC and we mostly live in login nodes; our sessions are limited to 8 hours which makes setting up such a daemon a bit tricky. Could probably set up somewhere else a cronjob to connect and start it, but it feels a bit cumbersome.

[–] CallMeAl@piefed.zip -1 points 1 week ago (1 children)

Running the inotify script as a service as root would require only one instance. You could trigger it on close_write and then run setfacl to add ACL entries to the new file for all the share users.

If you can't add a daemon or service to the system then you can skip inotify and just slam a cron job at it every minute to find new files and update their perms if needed. Ugly but effective.

Another option to consider: You could write a little script that changes umask, copies files, and changes it back. Tell people they must use that "share_cp" script to put files into the share dir.

[–] ranzispa@mander.xyz 2 points 1 week ago

We can not setup a common group, no way we get root privileges. A cron job would not work either: it is a cluster with many nodes, of which many login nodes. Cron jobs do not work on such systems.

A share_cp script would in fact be a good solution, I may try that and see if people pick it up.