昨天安裝完成pg 9.5后，啟動報錯：
FATAL: could not create semaphores: No space left on device
DETAIL: Failed system call was semget(xxxxxxxxxx).
HINT: This error does *not* mean that you have run out of disk space. It occurs when either the system limit for the maximum number of semaphore sets (SEMMNI), or the system wide maximum number of semaphores (SEMMNS), would be exceeded. You need to raise the respective kernel parameter. Alternatively, reduce PostgreSQL's consumption of semaphores by reducing its max_connections parameter.
查看報錯日志是由於內核的相關配置參數設置過小引起的。
這里是共享內存段的限制，簡單介紹一下
如果數據庫報FATAL: could not create shared memory segment:Cannot allocate memory 錯誤，可以考慮修改以下相關參數
#ipcs -lm ------ Shared Memory Limits -------- max number of segments = 4096 max seg size (kbytes) = 67108864 max total shared memory (kbytes) = 17179869184 min seg size (bytes) = 1
#cat /proc/sys/kernel/shmmax 68719476736
SHMMAX 單個共享內存段最大字節數
# cat /proc/sys/kernel/shmmni 4096
SHMMNI 共享內存段最大個數
# cat /proc/sys/kernel/shmall 4294967296
SHMALL系統中共享內存也總數，至少為ceil(shmmax/PAGE_SIZE)
獲取page_size值
# getconf PAGE_SIZE 4096
可以根據實際情況修改以上參數值，在/etc/sysctl.conf配置文件中
今天遇到的錯誤，主要解決以下參數的限制才能解決我們數據庫啟動的報錯
# ipcs -ls ------ Semaphore Limits -------- max number of arrays = 1280 max semaphores per array = 50100 max semaphores system wide = 64128000 max ops per semop call = 50100 semaphore max value = 32767 # cat /proc/sys/kernel/sem SEMMSL SEMMNS SEMOPM SEMMNI 50100 128256000 50100 2560
SEMMSL 每個信號量set中信號量最大個數
SEMMNS linux系統中信號量最大個數
SEMOPM semop系統調用允許的信號量最大個數設置，設置成和SEMMSL一樣即可
SEMMNI linux系統信號量set最大個數
所以SEMMNS=SEMMSL*SEMMNI
所以要么增大信號量，要么減少max_connect參數
這里我選擇增大信號量
修改 vi /etc/sysctl.conf 的以下參數
kernel.sem = 50100 128256000 50100 2560
ipcs -ls
------ Semaphore Limits --------
max number of arrays = 2560
max semaphores per array = 50100
max semaphores system wide = 128256000
max ops per semop call = 50100
semaphore max value = 32767
重新啟動數據庫后無報錯，數據庫可以正常啟動。
下面是官方文檔中對s
emaphores相關參數的說明：
| Name | Description | Reasonable values |
|---|---|---|
| SHMMAX | Maximum size of shared memory segment (bytes) | at least 1kB (more if running many copies of the server) |
| SHMMIN | Minimum size of shared memory segment (bytes) | 1 |
| SHMALL | Total amount of shared memory available (bytes or pages) | if bytes, same as SHMMAX; if pages, ceil(SHMMAX/PAGE_SIZE) |
| SHMSEG | Maximum number of shared memory segments per process | only 1 segment is needed, but the default is much higher |
| SHMMNI | Maximum number of shared memory segments system-wide | like SHMSEG plus room for other applications |
| SEMMNI | Maximum number of semaphore(打旗語) identifiers (i.e., sets) | at least ceil((max_connections + autovacuum_max_workers + max_worker_processes + 5) / 16) |
| SEMMNS | Maximum number of semaphores system-wide | ceil((max_connections + autovacuum_max_workers + max_worker_processes + 5) / 16) * 17 plus room for other applications |
| SEMMSL | Maximum number of semaphores(信號) per set | at least 17 |
| SEMMAP | Number of entries in semaphore map | see text |
| SEMVMX | Maximum value of semaphore | at least 1000 (The default is often 32767; do not change unless necessary) |
參考：
http://blog.163.com/dazuiba_008/blog/static/363349812016314739538/
http://www.postgresql.org/docs/9.4/static/kernel-resources.html#SYSVIPC-PARAMETERS