From a C Program to a Linux Utility
Making the daemon start automatically
I did not want to run ./clipd & every time I logged into Ubuntu.
I wanted the daemon to behave like a normal background service.
Since this is a user application, I used a systemd user service.
I turned this into a systemd service unit:
The exact install path and options can differ depending on the package layout, but the basic idea is simple.
Systemd takes care of:
- starting the daemon
- restarting it after failure
- keeping it attached to the user session
- integrating it with normal Linux service management
Why a user service instead of a system service?
This was another design decision I had to take. The clipboard should be user-specific. Reason is simply the seperation for different users. A system service would also make the privilege model more complicated.
A user service gives me:
User A
└── clipd
└── User A clipboard
User B
└── clipd
└── User B clipboard
The .deb package
I packaged the project as a Debian package because Ubuntu is my primary target.
The package layout is roughly:
/
├── usr/
│ └── bin/
│ ├── clipd
│ └── clipboard
│
└── usr/
└── lib/
└── systemd/
└── user/
└── clipd.service
Performance
One of my goals was to keep the daemon tiny.
There is:
- no database
- no background polling timer
- no heavy GUI
- no network stack
- no giant runtime
The daemon ended up using roughly 400 KB of RAM in my observed setup. This is way good and almost nothing.
Learnings
Although not heavy in RAM usage, this was one of the most heavy projects on my head, in the sense that it taught me a LOT and there was so much for me to take in. I learnt about display servers, IPC, Security, uinput, systemd, deb packaging, etc…
I started with a small quality-of-life problem. I finished with a much better understanding of Linux.
And, finally, my muscle memory is at peace.
Overall, I’d say it was a Win V situation….
( get it? Win V, Win WIn, WIn + V )