RetroFedWhat am I doing wrong with Linux/NAS permissions?
IronKrillAn alternative title would be “Convince me to not just give up and 777 everything” (everything that wouldn’t immediately break from forced permissions, that is).
I’ve been running a Linux NAS, specifically TrueNAS, for a few years now and it is a non-stop fight with permissions. The general recommendation I hear is to set different users for apps such as Docker to prevent permission over-reach, in the same vein as avoiding use of root, and some things simply require multiple users. Which I get.
My problems begin when I try to provide access to the same file/folders across multiple users. Say I want my Jellyfin library to be editable by my personal account, or allow an app access to my camera roll folder. I often find the way programs and Linux user permissions work is that upon file creation they set too restrictive permissions (different owner and ignoring the existing group/other perms). This then causes errors when another user tries to access or change the file later. It isn’t always a constant, but it comes up very often that I am fighting owner / permission issues.
I have attempted to fix this with an hourly cron job as root that performs chown and chmod on certain directories, but this is 1) a pain to set up and manage, and 2) I have to sometimes wait up to 59 minutes to access the files or have a cron job running every minute or so on a terabyte of files (ew). I felt that this surely can’t be the intended way.
Thus I’m currently trying ACLs via the TrueNAS GUI. Specifically I have used NFSv4 ACLs because they have “Inherit” flags which allows me to enforce the user/owner/permissions upon file creation. This solution works beautifully for a single dataset/single ACL of my personal files! I can copy, paste, and edit to my heart’s content without anything setting it’s own permissions and fucking it up. The annoyances with this solution begin when using it on sshfs¹ mounted folders in Dolphin, where trying to cut+paste a file from Folder A with ACL 1 to Folder B with ACL 2 throws permission errors. I then have to copy and delete separately which is annoying, especially when you forgot you’re going across two different ACLs. I also expect this to break upon use with certain picky Docker apps unless I get the ACL perfect, but I haven’t tried the tricky ones yet.
So really my question is this: what am I missing? Surely I’m not expected to sudo chown && sudo chmod every other day because a user account decided to set 755 instead of 775 like every other file in the directory, or because they set their personal user group instead of the example_user group?
Footnote ¹: sshfs
I use sshfs for a few reasons:
- SMB is slow, case insensitive, and does not work with many Linux filenames (they display as e.g
_GFBV4~O.JPG). - NFS does not display child filesystems, which ZFS datasets are treated as since they’re mounts. I don’t want to setup a cross-device mount for every dataset.
- I have heard sshfs is generally the fastest.
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No, you are not expected to cronjob the chmod command.
You want “umask”. That’s the term, you can google it for more info.
Basically, it’s the setting that controls what the default permissions are for the files created by a process.
Jellyfins umask is configurable using the systemd unit file. Arr stack umasks are somewhere in their settings… Etc.
It is process specific, and something you configure for each application. Owner is whatever user runs the process, and same goes for group.
Group does not need to be same as user. You can run jellyfin with a “jellyfin” user and “media” group, so that some other app managing the media files can deal with jellyfins files by running under a different user but the same “media” group.
As long as you set their umasks to allow group access they will then always be able to pass files and directeries between them.
I’ve no experience with ACLs. I’ve used SMB, and SSHFS to a lesser extent, and always with very simple setups.
My user accessing my own users files via SMB, and ssh only via the admin user and as such with root level access.
But generally, unix-style permissions should allow you to be able to set things up in whatever way you might need. Getting there can be complex, but there is always a way to configure what permissions directories and files will have when created, and hence what users/groups can access them.
Also, sometimes the answer is to edit the groups. Such as adding a user being used to access a share to the relevant groups, instead of messing with owners or groups of existing files and directories.
Or, creating a whole new group (like “pictures” for your camera roll thing) which you add all the relevant users to (yourself, and whatever apps will be accessing the relevant directories). Plus then configure umasks so that files actually default to allowing group level access.
I see. I’ve heard of umask but skipped over it since it still allows permissions to become out of sync in the directories, hence my falling back on cron jobs. It would help though, but my personal user acting in this directory would still create files as my_user:my_group, even if I am part of the media_group. Does that mean I am doomed to go into CLI and
chown :media_groupeverytime I copy a movie into my movie directory?No, there’s a longstanding pattern to solve the group issue.
1-3 ensures everyone that needs to write can, and 4 will make any file created in that dir inherit the group from the dir instead of the creating user. So future files will still be writable due to group write perms.
That sounds promising, I’ll take a look at it.
Note, #4 will not apply to files MOVED into the directory. Only files that count as “created” there (like a copy operation).
No.
Assuming you’re accessing your files via network mounts, those file are being created by the relevant SMB/NFS/SSH daemon. ALL FILES are created by some process or other. If you click “new file” in Dolphin, that process is Dolphin.
Which means there is a umask you can configure.
My network SMB mount that leads to my jellyfin libraries is configured (on the server) to access the filesystem under my user and the shared media group. Hence files it “creates” are always done so with correct permissions. User, group and umask are configurable for each share.
This way, I can copy files from a share containing “my” files, into the media share, and have the owner, group and umask automatically “translate” into what they should be in either direction. Theres not really a way to do that directly on the system. It’s something you can only really set up when moving files around between the shares and hence their respective environments.
If I did the move in the terminal directly on the host system, shit would instantly break.
Files and directories can only have one owner for user and group, each. If files you create belonged to every group you are in, that’d be a permission nightmare, so by default, the group permission is “unused” (it just gets set to the same as your user).
You could add the application that needs to access files created by you to your user group, but that’s a lot more permissive than it needs to be (it gets to access all your files with group access granted).
If you’re managing files via network shares, the solution is in their settings.
If you’re managing files on the system directly, that’s trickier. New files can be made to inherit the group of the parent directory (edit: other commentor), which solves your problem only some of the time, as it won’t affect files you move into the folder. In those cases you still have to fix the group after moving. That, or copy instead of move.
Bottom line: You’re not really supposed to manage this stuff directly. When you go in and create files directly on the host system, you are bypassing the systems that would normally set permissions inside a share or directory that is being accessed by multiple applications, users, and services.
Making the default of files created in such a way non-permissive, is by design. That you have to manually correct the group permissions on a file you just moved in from another permission environment, is as it should be.
Ugh I have the same problems. My synology nas whenever I Mount it I can’t do anything to it unless I open the folder as root. I also can’t download directly to it because of this. Its hard.
The solution you’re looking for is to have a group that all those users belong to, and make the files have RW for that group.
The solution you should do instead is to run things inside docker, so each one gets an extra isolation layer, but all can write to the same files easily.
Do not 777 everything. Never. Unix file permissions actually work, are pretty simple when you’ve worked with them, and most importantly are a huge part of your systems security as a whole. Running with broken permissions is a surefire way to get data exfiltrated or to provide an entry point for an attacker. Do not chmod everything, and do not run lax permissions.
Let’s say you have a service-A and a service-B running, each with their own user. A produces files into a shared folder, B consumes them. The proper Unix way of this is:
The chmod g+s is the magic bit you’re missing. With this set, any file created will inherit the group ownership from its parent directory - so anything service-A creates will default to the permissions you’ve set up for the group on the folder, and since service-B is also in that group, files are readable.
This pattern applies to any number of services and in any deployment model.