共享内存就是进程之间可以共享的一段内存，通过一个唯一的KEY值绑定
shmget()创建或获取
shmat()连接
shmdt()断连
共享内存的访问涉及同步措施，通常与信号灯一起使用
用ipcs -m命令可以查看系统中已有的共享内存段
/proc/sys/kernel/shm开头的几个文件是共享内存的参数
共享内存的访问涉及同步措施，通常与信号灯一起使用
用ipcs -m命令可以查看系统中已有的共享内存段
ipcs -m 看Shared Memory 共享内存
ipcs -q 看Message Queues 消息队列
ipcs -s 看Semaphore Arrays 信号量
使用命令：ipcs -al
------ Shared Memory Limits --------
max number of segments = 4096
max seg size (kbytes) = 4091826
max total shared memory (pages) = 2097152
min seg size (bytes) = 1
1. Linux Check Memory Usage
by VIVEK GITE on APRIL 6, 2006 · 36 COMMENTS
How do I check used and free RAM memory usage under Linux operating systems using command line and GUI tools?
Linux comes with different set of commands to check memory usage. The free command displays the total amount of free and used physical and swap memory in the system, as well as the buffers used by the kernel. The vmstat command reports information about processes, memory, paging, block IO, traps, and cpu activity. Finally, you can use the top command which provides a dynamic real-time view of a running system. It can display system summary information as well as a list of tasks currently being managed by the Linux kernel.
free command
Display free memory size in MB:
$ free -mOutput:
total used free shared buffers cached
Mem: 750 625 125 0 35 335
-/+ buffers/cache: 254 496
Swap: 956 0 956Displays a line containing the totals memory in MB:
$ free -t -m
Output:
total used free shared buffers cached
Mem: 750 625 125 0 35 335
-/+ buffers/cache: 253 496
Swap: 956 0 956
Total: 1707 625 1082