Why does transmission adds a new user to the system?

Question

When I installed transmission, I've seen here that I need to change the ownership of some groups to able this to work with my raspberry pi. First of all: why does transmission adds a new user to the system? I tried to set the downloads folder of transmission to my USB flash drive but I get a permission error. So I need to change who owns the folder of the pen drive, rigth? But who owns it? I just plugged my pen drive, I've never set nobody to own it.

Also, why he calls it "debian-transmission group". Isn't debian-transmission an user?

THe tutorial is basically saying I need to change the ownership of /media/MyPenDrive to the debian transmission user?

Then he says:

grant write access to the group

sudo chmod 770 /home/chen/TV\ shows

Isn't the group "debian-transmission"? Why is he granting write access to the folder? When he grants access to a folder, he grants access to everybody who owns it? Shouldn't I be able to give different permissions to different users who can access the folder?

Answer 1

You've asked a few questions.

Why does installing transmission create a new user?

For security. Basically, by running Transmission as its own user, its ability to touch other users' data on the system (such as your user) is greatly limited. If there is a security flaw in Transmission, a cracker who exploited it would find it much more difficult, if not impossible, to steal, modify, etc. your private data.

Isn't debian-transmission a user?

Yes, it is. It is a group as well. It's pretty common for a user to have a group with the same name (your user probably does too—check by running id for example).

Changing the owner of the flash drive

How to do this depends on if the flash drive is formatted as FAT32 (Windows compatible) or ext2/3/4/btrfs/etc. FAT32 doesn't support permissions; the mount options specify which users and group own the files, and the permissions. You'll have to modify the configuration of whatever is mounting it (if its from /etc/fstab, that's easy: just add the uid=, gid=, etc. options; see "Mount options for fat" in the mount(8) manpage). If it is a Unix filesystem (like ext2/3/4, btrfs, etc.) then the chgrp, chmod, etc. will work.

Note: files and directories have both an owning user and an owning group. They can be different. If you've ever wondered why ls -l shows your username twice, the second one is actually that group with the same name.

In short, yes, you need the debian-transmission user or group to have write access to whatever directory (and files) it is going to save downloads to. You can also use POSIX ACLs (setfacl) to grant those permissions without changing the ownership, if supported by the filesystem (and all the common Linux one's support it).