The mode member of the ipc_perm structure defines, with its lower nine bits, the access permissions to the resource for a process executing an ipc system call. The permissions are interpreted as follows:

Bits 0100, 0010, and 0001 (the execute bits) are unused by the system. Furthermore "write" effectively means "alter" for a semaphore set.

The same system header file defines also the following symbolic constants:

Note that IPC_PRIVATE is a key_t type, whereas all the others symbolic constants are flag fields ORable into an int type variable.

MESSAGE QUEUES

A message queue is uniquely identified by a positive integer (its msqid) and has an associated data structure of type struct msquid_ds, defined in <sys/msg.h>, containing the following members:

struct ipc_perm msg_perm;

ushort msg_qnum; /* no of messages on queue */

ushort msg_qbytes; /* bytes max on a queue */

ushort msg_lspid; /* pid of last msgsnd call */

ushort msg_lrpid; /* pid of last msgrcv call */

time_t msg_stime; /* last msgsnd time */

time_t msg_rtime; /* last msgrcv time */

time_t msg_ctime; /* last change time */

SEMAPHORE SETS

A semaphore set is uniquely identified by a positive integer (its semid) and has an associated data structure of type struct semid_ds, defined in <sys/sem.h>, containing the following members:

struct ipc_perm sem_perm;

time_t sem_otime; /* last operation time */

time_t sem_ctime; /* last change time */

ushort sem_nsems; /* count of sems in set */

A semaphore is a data structure of type struct sem containing the following members:

ushort semval; /* semaphore value */

short sempid; /* pid for last operation */

ushort semncnt; /* no. of awaiting semval to increase */

ushort semzcnt; /* no. of awaiting semval = 0 */

SHARED MEMORY SEGMENTS

A shared memory segment is uniquely identified by a positive integer (its shmid) and has an associated data structure of type struct shmid_ds, defined in <sys/shm.h>, containing the following members:

struct ipc_perm shm_perm;

int shm_segsz; /* size of segment */

ushort shm_cpid; /* pid of creator */

ushort shm_lpid; /* pid, last operation */

short shm_nattch; /* no. of current attaches */

time_t shm_atime; /* time of last attach */

time_t shm_dtime; /* time of last detach */

time_t shm_ctime; /* time of last change */

SEE ALSO

ftok(3), msgctl(2), msgget(2), msgrcv(2), msgsnd(2), semctl(2), semget(2), semop(2), shmat(2), shmctl(2), shmget(2), shmdt (2)

Linux 0.99.13, 1 November 1993

issue

issue—Issue identification file.

DESCRIPTION

The file /etc/issue is a text file that contains a message or system identification to be printed before the login prompt. It may contain various @char and \char sequences if supported by getty(1).

FILES

/etc/issue

SEE ALSO

getty(1), motd(5)

Linux, 24 July 1993

lilo.conf

lilo.conf—Configuration file for LILO.

DESCRIPTION

This file, by default /etc/lilo.conf, is read by the boot loader installer LILO (see lilo(8)).

It might look as follows:

boot = /dev/hda

delay = 40

compact

vga = normal

root = /dev/hda1

read-only

image = /zImage-1.5.99

        label = try

image = /zImage-1.0.9

        label = 1.0.9

image = /tamu/vmlinuz

        label = tamu

        root = /dev/hdb2

        vga = ask

other = /dev/hda3

        label = dos

        table = /dev/hda

This configuration file specifies that LILO uses the Master Boot Record on /dev/hda. (For a discussion of the various ways to use LILO and the interaction with other operating systems, see user.tex from the LILO documentation.)

When booting, the boot loader will wait 4 seconds (40 deciseconds) for you to press Shift. If you don't, then the first kernel image mentioned (/zImage-1.5.99, which you probably installed just 5 minutes ago) will be booted. If you do, the boot loader will ask you which image to boot. In case you forgot the possible choices, press Tab (or ? if you have a U.S. keyboard), and you will be presented with a menu. You now have the choice of booting this brand new kernel, an old trusted kernel, or a kernel on another root file system (just in case you did something stupid on your usual root) or booting a different operating system. There can be up to 16 images mentioned in lilo.conf.

As can be seen previously, a configuration file starts with a number of global options (the top six lines in the example), followed by descriptions of the options for the various images. An option in an image description will override a global option.