linux进程生命周期

使用ps命令查看进程时，会发现状态上面有其他符号，比如 S+、Z+ 等，这个 + 是啥意思呢，其实man ps中就有描述，只是我们从来都没认真看说明文档：

PROCESS STATE CODES
Here are the different values that the s, stat and state output specifiers (header "STAT" or "S") will display to describe the state of a process:

               D    uninterruptible sleep (usually IO)
I    Idle kernel thread
R    running or runnable (on run queue)
S    interruptible sleep (waiting for an event to complete)
T    stopped by job control signal
t    stopped by debugger during the tracing
W    paging (not valid since the 2.6.xx kernel)
X    dead (should never be seen)
Z    defunct ("zombie") process, terminated but not reaped by its parent

For BSD formats and when the stat keyword is used, additional characters may be displayed:

               <    high-priority (not nice to other users)
N    low-priority (nice to other users)
L     has pages locked into memory (for real-time and custom IO)
s     is a session leader
l     is multi-threaded (using CLONE_THREAD, like NPTL pthreads do)
+    is in the foreground process group