ftok

I am using ftok() to generate identifiers for shared memory segments used by a C application. I am having problems, where on one box I am getting collisions with the identifiers used by root. I can fix it in this instance by hacking the code, but I would like a more robust solution. The application is installed into its own logical volume, and the path supplied to ftok is the binaries directory for the application (within that lv). The IDs supplied start at 1 and there are usually half a dozen or so. I've tracked down that ftok will do something like this: (id & 0xff) << 24 | (st.st_dev & 0xff

When using shared memory, why should we care about creating a key key_t ftok(const char *path, int id); in the following bit of code? key_t key; int shmid; key = ftok("/home/beej/somefile3", 'R'); shmid = shmget(key, 1024, 0644 | IPC_CREAT); From what I've come to understand, what is needed to access a given shared memory is the shmid , not the key. Or am I wrong? If what we need is the shmid , what is the point in not just creating a random key every time? Edit @ Beej's Guide to Unix IPC one can read: What about this key nonsense? How do we create one? Well, since the type key_t is actually

I have started reading message queues one of the IPC mechanism on Linux .But at very first step I have some very basic questions. Use of ftok() to generate unique ID (key) and what is unique ID which is to be generated. Can't we use simple a number to get our keys rather than using ftok() ? What is the purpose of the argument key in the msget function? #include "sys/msg.h" key = ftok("/home/beej/somefile", 'b'); msqid = msgget(key, 0666 | IPC_CREAT); What is the difference between msqid and key ? The ftok function creates a sort of identifier to be used with the System V IPC functions ( semget