Trial and error
The simplest and more robust method is to probe if you can allocate these resources, i.e.:
int shmid = shmget(key, LARGE_BUFFER_SIZE, 0644 | IPC_CREAT);
void* data = shmat(shmid, NULL, 0);
if (data == (char *)(-1)) {
/* Log an error and exit */
}
I.e. Oracle Database does that.
Linux
On Linux these limits are handled via sysctl:
$ /usr/sbin/sysctl kernel.shmmax
kernel.shmmax = 18446744073709551615
$ /usr/sbin/sysctl kernel.sem
kernel.sem = 250 256000 32 1024
^ SEMMSL ^ SEMMNI
You can get sysctl parameters from /proc/sys:
$ cat /proc/sys/kernel/sem
250 256000 32 1024
$ cat /proc/sys/kernel/shmmax
18446744073709551615
Solaris before 10
In Solaris before 10 kernel parameters were used. They are set in /etc/system. You can get actual values from kernel, but only when shmsys and semsys modules are loaded (Solaris lazy-loads them on first syscall):
# modload /kernel/sys/sparcv9/semsys
# modload /kernel/sys/sparcv9/shmsys
# echo 'shminfo_shmmax/J' | mdb -k
shminfo_shmmax:
shminfo_shmmax: 800000
# echo 'seminfo_semmni/J' | mdb -k
seminfo_semmni:
seminfo_semmni: a0000003c
Note that I used /J modifier in mdb which dumps 8-byte in hexademical. On 32-bits builds, you're probably will need /X which dumps 4-bytes.
Solaris 10 and later
Solaris 10 introduced projects, that allow to set these limits with granularity of user or even a process. Use prctl to get appropriate limits:
# prctl -n project.max-shm-memory $$
process: 3451: bash
NAME PRIVILEGE VALUE FLAG ACTION RECIPIENT
project.max-shm-memory
privileged 474MB - deny -
system 16,0EB max deny -
# prctl -n project.max-sem-ids $$
process: 3451: bash
NAME PRIVILEGE VALUE FLAG ACTION RECIPIENT
project.max-sem-ids
privileged 128 - deny -
system 16,8M max deny -
# prctl -n process.max-sem-nsems $$
process: 3451: bash
NAME PRIVILEGE VALUE FLAG ACTION RECIPIENT
process.max-sem-nsems
privileged 512 - deny -
system 32,8K max deny -
priviliged values is what you seek
