Linux – How to allow users to transfer files to other users on linux

filesystemshpclinux

We have an environment of a few thousand users running applications on about 40 clusters ranging in size from 20 compute nodes to 98,000 compute nodes. Users on these systems generate massive files (sometimes > 1PB) controlled by traditional unix permissions (ACLs usually aren't available or practical due to the specialized nature of the filesystem).

We currently have a program called "give", which is a suid-root program that allows a user to "give" a file to another user when group permissions are insufficient. So, a user would type something like the following to give a file to another user:

> give username-to-give-to filename-to-give ...

The receiving user can then use a command called "take" (part of the give program) to receive the file:

> take filename-to-receive

The permissions of the file are then effectively transferred over to the receiving user.

This program has been around for years and we'd like to revisit things from a security and functional point of view.

Our current plan of action is to remove the bit rot in our current implementation of "give" and package it up as an open source app before we redeploy it into production.

Does anyone have another method they use to transfer extremely large files between users when only traditional unix permissions are available?

Best Answer

As xryl669 says you can use a directory to actually share the files. It should look like this:

$ ls -ld shared
drwxrws--- 2 root usergroup 4096 somedate shared
$ ls -l shared
drwx-wx--- 2 user1 usergroup 4096 somedate user1
drwx-wx--- 2 user2 usergroup 4096 somedate user2
drwx-wx--- 2 user3 usergroup 4096 somedate user3
drwx-wx--- 2 user4 usergroup 4096 somedate user4

The give command becomes

#!/bin/sh
#Use a random suffix to prevent guessing
RANDOM=$(dd if=/dev/urandom count=4 2> /dev/null | sha512sum | cut -d' ' -f1)
NEWNAME=/path/to/shared/$2/$1$RANDOM
#Move the file
mv $1 $NEWNAME
#Make it readable
chmod 440 $NEWNAME

The take command looks something like this:

$ cd /path/to/shared/user
$ ls
...
$ mv somefile ~
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