Solaris Inter-Process Communication (IPC) Interview Preparation Guide

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Maximum adjust-on-exit value. This should almost always be left alone. The default is 16384; the maximum is 32767.

Maximum value of a semaphore. This should never exceed 32767 (default value) unless SEM_UNDO is never used. The default is 32767; the maximum is 65535.

Number of bytes required for semume undo structures. This should not be tuned; it is set to semume x (1 + sizeof(undo)). The default is 96; the maximum is 2 GB.

Maximum number of undo structures per process. This should be set to semopm times the number of processes that will be using semaphores at any one time. The default is 10; the maximum is 2 GB.

Maximum number of semaphore operations that can be performed in each semop call. The default in Solaris 2.5.1-9 is 10, the maximum is 2 GB. Solaris 10 increased the default to 512.

Maximum number of semaphores per semaphore set. The default is 25, the maximum is 65535.

Maximum number of undo structures in the system. This should be set to semmni so that each control structure has an undo structure. The default is 30, the maximum is 2 GB.

Maximum number of semaphores in the system. Each structure uses 16 bytes. This parameter should be set to semmni x semmsl. The default is 60; the maximum is 2GB.

Maximum number of systemwide semaphore sets. Each control structure consumes 84 bytes. For Solaris 2.5.1-9, the default setting is 10; for Solaris 10, the default setting is 128. The maximum is 65535

This sets the number of entries in the semaphore map. This should never be greater than semmni. If the number of semaphores per semaphore set used by the application is "n" then set
semmap = ((semmni + n - 1)/n)+1
or more. Alternatively, we can set semmap to semmni x semmsl. An undersized semmap leads to "WARNING: rmfree map overflow" errors. The default setting is 10; the maximum for Solaris 2.6 is 2GB. The default for Solaris 9 was 25; Solaris 10 increased the default to 512. The limit is SHRT_MAX.

Maximum number of segments per process. It is usually set to shmmni, but it should always be less than 65535. Sun documentations suggests a maximum for this parameter of 32767 and a default of 8 for Solaris 2.5.1 and 2.6.

Maximum number of shared memory identifiers at any given time. This parameter is used by kernel memory allocation to determine how much size to put aside for shmid_ds structures. Each of these is 112 bytes and requires an additional 8 bytes for a mutex lock; if it is set too high, memory useage can be a problem. The maximum setting for this variable in Solaris 2.5.1 and 2.6 is 2147483648 (2GB), and the default is 100. For Solaris 10, the default is 128 and the maximum is MAXINT.

This is the smallest possible shared memory segment size. The default is 1 byte; this parameter should probably not be tuned.

This is the maximum size of a shared memory segment (ie the largest value that can be used by shmget). Its theoretical maximum value is 4294967295 (4GB), but practical considerations usually limit it to less than this. There is no reason not to tune this value as high as possible, since no kernel resources are allocated based on this parameter. Solaris 10 sets shmmax to 1/4 physical memory by default, vs 512k for previous versions.

Yes i think Solaris is having a brilliant future.