I need to make sure one process executes only in one instance at a time. On Windows you could use named mutex. But I have no idea what to use on Linux.
I think I've seen an approach were app creates an exclusive file, but I can't find it anymore. Do you use regular file functions, busy-loop?
If you only want one instance of your app running you can use a lock file. Open it with O_CREAT|O_EXCL flags and it will fail if the file already exists.
If you want to synchronize access to a file use flock. It is also possible to lock parts of files with fcntl. Flock is only for advisory locking meaning a program can ignore the locks and access it anyway. Mandatory locking is possible with fcntl but it requires a special mount option and special file permissions.
semget and semop can be used for interprocess synchronization too.
Interprocess mutexes are an optional part of POSIX (see _POSIX_THREAD_PROCESS_SHARED on the unistd.h page) and as they are implemented on Linux you can use them too - see examples.
