Capabilities
Core Technology
Everyone wants to be root, because root can do anything. But in fact, its powers are now split. Learn more in this overview of capability sets.
Today's Linux is somewhat like a famous sightseeing city you might have visited on your last vacation. There is a historic part that's of no practical use now, yet it is what keeps the city's identity. There are some well-known tourist spots that everybody seems to visit. And, finally, there are some secluded locations you never find in an advertisement in a travel agency. These are places a friend living there would show you, and they are essential for sensing a real spirit of the city, not its pamphlet picturesque image.
Okay, maybe I've taken the analogy a bit too far here. But if you agree to follow it for a second, capabilities would be one of these secluded locations. Introduced with Linux 2.2, they are what really tells if process X can do Y. Yet they are often lost in shadows of traditional Unix privileges, SELinux, eBPF, and many others. By the end of this Core Tech article, you'll know who really sets your limits in a city of Linux.
An All-Mighty Root (Actually, Not)
Back in ye olde days, the permission system of Linux was pretty much simple. A user with UID 0 – often called "root" – could do any privileged operation, and he wasn't subject to permission checks. Note it is the UID, not the name, which is important. A user called "val" with UID 0 holds all powers of root user as well.
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