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如何确定最大用户进程值？

tag-icon • tag-icon linux proc limit
如何确定最大用户进程值？

哪一个值是正确的？（或者都正确，但哪一个生效？）

$ cat /proc/sys/kernel/pid_max 
32768
$ ulimit -a |grep processes
max user processes              (-u) 77301
$ cat /proc/1/limits |grep processes
Max processes             77301                77301                p

答案1

所有值都是正确的并且具有不同的含义。/proc/sys/kernel/pid_max是 的最大值PID，ulimit -u是 的最大值number of processes。

从man 5 proc：

/proc/sys/kernel/pid_max (since Linux 2.5.34)
              This  file  specifies the value at which PIDs wrap around (i.e.,
              the value in this file is one greater  than  the  maximum  PID).
              The  default  value  for  this  file, 32768, results in the same
              range of PIDs as on earlier kernels.  On 32-bit platforms, 32768
              is  the  maximum  value for pid_max.  On 64-bit systems, pid_max
              can be set to any value up to 2^22 (PID_MAX_LIMIT, approximately
              4 million).

从man bash：

ulimit [-HSTabcdefilmnpqrstuvx [limit]]
              .....
              -u     The maximum number of processes available to a single user
              .....

笔记

当创建一个新进程时，它会被分配下一个可用的内核进程计数器数。当达到 时pid_max，内核将进程计数器重新启动到 300。从 linux 源代码，pid.c文件：

....
#define RESERVED_PIDS       300
....
static int alloc_pidmap(struct pid_namespace *pid_ns)                           
{                                                                               
    int i, offset, max_scan, pid, last = pid_ns->last_pid;                      
    struct pidmap *map;                                                         

    pid = last + 1;                                                             
    if (pid >= pid_max)                                                         
        pid = RESERVED_PIDS;

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