Linux查看指定进程占用的资源
查看指定进程占用的资源。
pidstat查看进程的CPU使用率
pidstat命令可以显示每个进程的在不同CPU状态中耗费的时间的百分比(1，每秒显示一次；-p，指定进程，如果不指定，显示所有进程)：
$ pidstat 1 -p 27936
Linux 3.10.0-693.11.6.el7.x86_64 (10.10.64.58) 12/04/2018 _x86_64_ (4 CPU)
05:00:59 PM UID PID %usr %system %guest %CPU CPU Command
05:01:00 PM 99 27936 0.00 0.00 0.00 0.00 0 openresty
05:01:01 PM 99 27936 0.00 0.00 0.00 0.00 0 openresty
05:01:02 PM 99 27936 0.00 0.00 0.00 0.00 0 openresty
pidstat查看进程的IO情况
pidstat，-d表示展示IO信息，1表示每秒输出一次，使用-p指定进程号，下面间隔 1 秒输出 3 组数据：
$ pidstat -d -p 4344 1 3
06:38:50 UID PID kB_rd/s kB_wr/s kB_ccwr/s iodelay Command
06:38:51 0 4344 0.00 0.00 0.00 0 app
06:38:52 0 4344 0.00 0.00 0.00 0 app
06:38:53 0 4344 0.00 0.00 0.00 0 app
pidstat查看进程的切换情况
pidstat -w -p 进程号可以显示指定进程的上下文切换情况：
$ pidstat -w 2 -p 426
Linux 4.20.12-1.el7.elrepo.x86_64 (10.10.64.58) 04/29/2019 _x86_64_ (4 CPU)
03:01:12 PM UID PID cswch/s nvcswch/s Command
03:01:14 PM 99 426 2.99 0.00 openresty
03:01:16 PM 99 426 2.50 0.00 openresty
03:01:18 PM 99 426 3.00 0.00 openresty
03:01:20 PM 99 426 2.00 0.00 openresty
-w参数的作用是显示进程切换状态，每一列的含义如下（可以在man pidstat中找到）：
-w Report task switching activity (kernels 2.6.23 and later only).
The following values may be displayed:
UID
The real user identification number of the task being monitored.
USER
The name of the real user owning the task being monitored.
PID
The identification number of the task being monitored.
cswch/s
Total number of voluntary context switches the task made per second.
A voluntary context switch occurs when a task blocks because it requires
a resource that is unavailable.
nvcswch/s
Total number of non voluntary context switches the task made per second.
A involuntary context switch takes place when a task executes for the duration
of its time slice and then is forced to relinquish the processor.
Command
The command name of the task.
需要注意自愿切换（cswch/s，voluntary context switches）和非自愿切换（nvcswch/s，non voluntary context switches）的区别。前者是因为需要的资源没有准备好，主动让出CPU发生的切换，后者是进程分配的时间片已经用完，被调度器强制切换。
pidstats -w显示的是进程的状态，如果要将线程一并显示出来，需要再加一个-t参数：
$ pidstat -wt
Average: UID TGID TID cswch/s nvcswch/s Command
Average: 0 3 - 3.92 0.00 ksoftirqd/0
Average: 0 - 3 3.92 0.00 |__ksoftirqd/0
Average: 0 9 - 45.59 0.00 rcu_sched
Average: 0 - 9 45.59 0.00 |__rcu_sched
Average: 0 13 - 1.96 0.00 ksoftirqd/1
Average: 0 - 13 1.96 0.00 |__ksoftirqd/1
Average: 0 17 - 0.49 0.00 migration/2
另外pidstat还有一个-u参数，可以一并输出进程和线程（加-t）的CPU使用情况：
[[email protected] ~]# pidstat -wt -u
Linux 3.10.0-693.11.6.el7.x86_64 (10.10.64.58) 12/04/2018 _x86_64_ (4 CPU)
04:21:56 PM UID TGID TID %usr %system %guest %CPU CPU Command
04:21:56 PM 0 1 - 0.02 0.01 0.00 0.03 0 systemd
04:21:56 PM 0 - 1 0.02 0.01 0.00 0.03 0 |__systemd
04:21:56 PM 0 2 - 0.00 0.00 0.00 0.00 0 kthreadd
04:21:56 PM 0 - 2 0.00 0.00 0.00 0.00 0 |__kthreadd
04:21:56 PM UID TGID TID cswch/s nvcswch/s Command
04:21:56 PM 0 1 - 1.75 0.00 systemd
04:21:56 PM 0 - 1 1.75 0.00 |__systemd
04:21:56 PM 0 2 - 0.01 0.00 kthreadd
04:21:56 PM 0 - 2 0.01 0.00 |__kthreadd
04:21:56 PM 0 3 - 2.53 0.00 ksoftirqd/0
lsof查看进程打开的文件
lsof查看进程打开的文件，-p指定进程号，注意必须是进程号，不能是线程号：
$ lsof -p 18940
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
python 18940 root cwd DIR 0,50 4096 1549389 /
python 18940 root rtd DIR 0,50 4096 1549389 /
…
python 18940 root 2u CHR 136,0 0t0 3 /dev/pts/0
python 18940 root 3w REG 8,1 117944320 303 /tmp/logtest.txt
strace查看进程发起的系统调用
strace跟踪进程的系统调用，-f 表示跟踪子进程和子线程，-T 表示显示系统调用的时长，-tt 表示显示跟踪时间：
$ strace -f -T -tt -p 9085
[pid 9085] 14:20:16.826131 epoll_pwait(5, [{EPOLLIN, {u32=8, u64=8}}], 10128, 65, NULL, 8) = 1 <0.000055>
[pid 9085] 14:20:16.826301 read(8, "*2\r\n$3\r\nGET\r\n$41\r\nuuid:5b2e76cc-"..., 16384) = 61 <0.000071>
[pid 9085] 14:20:16.826477 read(3, 0x7fff366a5747, 1) = -1 EAGAIN (Resource temporarily unavailable) <0.000063>
[pid 9085] 14:20:16.826645 write(8, "$3\r\nbad\r\n", 9) = 9 <0.000173>
[pid 9085] 14:20:16.826907 epoll_pwait(5, [{EPOLLIN, {u32=8, u64=8}}], 10128, 65, NULL, 8) = 1 <0.000032>
[pid 9085] 14:20:16.827030 read(8, "*2\r\n$3\r\nGET\r\n$41\r\nuuid:55862ada-"..., 16384) = 61 <0.000044>
[pid 9085] 14:20:16.827149 read(3, 0x7fff366a5747, 1) = -1 EAGAIN (Resource temporarily unavailable) <0.000043>
[pid 9085] 14:20:16.827285 write(8, "$3\r\nbad\r\n", 9) = 9 <0.000141>
[pid 9085] 14:20:16.827514 epoll_pwait(5, [{EPOLLIN, {u32=8, u64=8}}], 10128, 64, NULL, 8) = 1 <0.000049>
[pid 9085] 14:20:16.827641 read(8, "*2\r\n$3\r\nGET\r\n$41\r\nuuid:53522908-"..., 16384) = 61 <0.000043>
[pid 9085] 14:20:16.827784 read(3, 0x7fff366a5747, 1) = -1 EAGAIN (Resource temporarily unavailable) <0.000034>
[pid 9085] 14:20:16.827945 write(8, "$4\r\ngood\r\n", 10) = 10 <0.000288>
[pid 9085] 14:20:16.828339 epoll_pwait(5, [{EPOLLIN, {u32=8, u64=8}}], 10128, 63, NULL, 8) = 1 <0.000057>
[pid 9085] 14:20:16.828486 read(8, "*3\r\n$4\r\nSADD\r\n$4\r\ngood\r\n$36\r\n535"..., 16384) = 67 <0.000040>
[pid 9085] 14:20:16.828623 read(3, 0x7fff366a5747, 1) = -1 EAGAIN (Resource temporarily unavailable) <0.000052>
[pid 9085] 14:20:16.828760 write(7, "*3\r\n$4\r\nSADD\r\n$4\r\ngood\r\n$36\r\n535"..., 67) = 67 <0.000060>
[pid 9085] 14:20:16.828970 fdatasync(7) = 0 <0.005415>
[pid 9085] 14:20:16.834493 write(8, ":1\r\n", 4) = 4 <0.000250>