attr:
进程的属性
cmdline：
启动进程时执行的命令
cwd:
指向进程当前工作目录的软链
environ：
进程执行时使用的环境变量，文件内容使用null字节（'\0'）分隔，然后以null字节结束。因此获取进程使用的环境变量使用如下：
(cat /proc/pid/environ; echo) | tr '\000' '\n'
fd:
此目录包含进程打开的所有文件，文件名为文件描述符，目录中每个软连接都会指向进程打开的实际文件。
limits:
该文件存储了进程的软限制，硬限制等信息。
maps:
address perms offset dev inode pathname
08048000-08056000 r-xp 00000000 03:0c 64593 /usr/sbin/gpm
4001f000-40135000 r-xp 00000000 03:0c 45494 /lib/libc-2.2.4.so
* address：进程占用的地址空间。
* perms：权限集
r = read
w = write
x = execute
s = shared
p = private (copy on write)
* offset：文件偏移量。
* dev:为设备（major:minor）
* inode：设备上的inode。0为没有inode关联互内存区域，通常为：BSS（uninitialized data）
root:
指向进程更目录的软链
smaps:
This file shows memory consumption for each of the process's mappings. For each of mappings there is a series of lines such as the following:
08048000-080bc000 r-xp 00000000 03:02 13130 /bin/bash
Size: 464 kB
Rss: 424 kB
Shared_Clean: 424 kB
Shared_Dirty: 0 kB
Private_Clean: 0 kB
Private_Dirty: 0 kB
The first of these lines shows the same information as is displayed for the mapping in /proc/[pid]/maps. The remaining lines show the size of
the mapping, the amount of the mapping that is currently resident in RAM, the number of clean and dirty shared pages in the mapping, and the
number of clean and dirty private pages in the mapping.
This file is only present if the CONFIG_MMU kernel configuration option is enabled.
status：
Name: bash
State: S (sleeping)
Tgid: 3515
Pid: 3515
PPid: 3452
TracerPid: 0
Uid: 1000 1000 1000 1000
Gid: 100 100 100 100
FDSize: 256
Groups: 16 33 100
VmPeak: 9136 kB
VmSize: 7896 kB
VmLck: 0 kB
VmHWM: 7572 kB
VmRSS: 6316 kB
VmData: 5224 kB
VmStk: 88 kB
VmExe: 572 kB
VmLib: 1708 kB
VmPTE: 20 kB
Threads: 1
SigQ: 0/3067
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000010000
SigIgn: 0000000000384004
SigCgt: 000000004b813efb
CapInh: 0000000000000000
CapPrm: 0000000000000000
CapEff: 0000000000000000
CapBnd: ffffffffffffffff
Cpus_allowed: 00000001
Cpus_allowed_list: 0
Mems_allowed: 1
Mems_allowed_list: 0
voluntary_ctxt_switches: 150
nonvoluntary_ctxt_switches: 545
The fields are as follows:
* Name: Command run by this process.
* State: Current state of the process. One of "R (running)", "S (sleeping)", "D (disk sleep)", "T (stopped)", "T (tracing stop)", "Z (zom-
bie)", or "X (dead)".
* Tgid: Thread group ID (i.e., Process ID).
* Pid: Thread ID (see gettid(2)).
* TracerPid: PID of process tracing this process (0 if not being traced).
* Uid, Gid: Real, effective, saved set, and file system UIDs (GIDs).
* FDSize: Number of file descriptor slots currently allocated.
* Groups: Supplementary group list.
* VmPeak: Peak virtual memory size.
* VmSize: Virtual memory size.
* VmLck: Locked memory size.
* VmHWM: Peak resident set size ("high water mark").
* VmRSS: Resident set size.
* VmData, VmStk, VmExe: Size of data, stack, and text segments.
* VmLib: Shared library code size.
* VmPTE: Page table entries size (since Linux 2.6.10).
* Threads: Number of threads in process containing this thread.
* SigPnd, ShdPnd: Number of signals pending for thread and for process as a whole (see pthreads(7) and signal(7)).
* SigBlk, SigIgn, SigCgt: Masks indicating signals being blocked, ignored, and caught (see signal(7)).
* CapInh, CapPrm, CapEff: Masks of capabilities enabled in inheritable, permitted, and effective sets (see capabilities(7)).
* CapBnd: Capability Bounding set (since kernel 2.6.26, see capabilities(7)).
* Cpus_allowed: Mask of CPUs on which this process may run (since Linux 2.6.24, see cpuset(7)).
* Cpus_allowed_list: Same as previous, but in "list format" (since Linux 2.6.26, see cpuset(7)).
* Mems_allowed: Mask of memory nodes allowed to this process (since Linux 2.6.24, see cpuset(7)).
* Mems_allowed_list: Same as previous, but in "list format" (since Linux 2.6.26, see cpuset(7)).
* voluntary_context_switches, nonvoluntary_context_switches: Number of voluntary and involuntary context switches (since Linux 2.6.23).
task：
进程包含的线程，子目录名是线程的ID
