Set umask for systemd service, but files created by the process are still using the default

Question

This is the unit for the Transmission torrent client, which was compiled and installed from source.

/etc/systemd/system/transmission.service:

[Unit]
Description=Start the Transmission daemon
After=network.target

[Service]
Type=simple
User=_transmission
ExecStart=/usr/local/bin/transmission-daemon --foreground
UMask=0002

[Install]
WantedBy=multi-user.target

I need it to use umask 0002, but it still creates new files with the default 0022.

_transmission is a system user, but it has a home folder. All other options are default. It has no default group (gid "nogroup").

Things I've tried

• systemctl daemon-reload
• systemctl restart transmission.service
• Reboot

System info

• Hardware: Raspberry Pi 4B (arm64)
• OS: Raspberry Pi OS (based on Debian bookworm)
• systemd 252

Answer 1

Well, it seems Transmission overrides the umask internally, so systemd cannot change it. Transmission lets you change the umask with a configuration option, which is documented here.

umask: String (default = "022") Sets Transmission's file mode creation mask. See the umask(2) manpage for more information.

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I was also trying to do the same for the Syncthing process, and the systemd method works. It's even documented here. However, it only honors the umask if you set "ignore permissions" on the folders.

If you enabled the Ignore Permissions option in the Syncthing client’s folder settings, then you will also need to add the line UMask=0002 (or any other umask setting you like) in the [Service] section of the [email protected] file.