Linux trivia

• Moving a file generally does not require +w permission on the file itself… unless that file is a directory, in which case it is required in order to update the .. entry. (blog)
• Whether you can access a path depends on how you name it. (blog)
• Signal masks and ignored signals are inherited across both fork and exec; this can cause problems if a parent process ignores or masks signals that a child process expects to receive, and can make signalfd challenging to use correctly.
• Linux allows different threads of a process to have different UIDs and GIDs, but POSIX doesn't, so NPTL (the Linux pthreads implementation) uses signals to ensure that a credential change in one thread propagates to all others.