Linux 常用排除问题命令
准备工作：
- Centos7 上装好jdk
- 写一个死循环程序
JavaDemo.java
import java.util.Random;
public class JavaDemo {
public static void main(String[] args) {
while(true) {
System.out.println(new Random().nextInt(77778888));
}
}
}
终端命令行执行：
# 编译
javac JavaDemo.java
# 运行
java JavaDemo
整体查看的 top 命令
直接执行top命令
top
top - 15:00:07 up 3:39, 3 users, load average: 0.89, 0.64, 0.35
Tasks: 260 total, 2 running, 258 sleeping, 0 stopped, 0 zombie
%Cpu(s): 7.2 us, 5.9 sy, 0.0 ni, 86.8 id, 0.1 wa, 0.0 hi, 0.0 si, 0.0 st
KiB Mem : 1863252 total, 111108 free, 916128 used, 836016 buff/cache
KiB Swap: 2097148 total, 2095100 free, 2048 used. 641492 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
16970 wsh 20 0 3244408 94828 12524 S 62.5 5.1 0:47.51 java
15799 wsh 20 0 771448 37496 20304 R 39.2 2.0 1:33.38 gnome-terminal-
13628 wsh 20 0 4244796 252816 69964 S 4.7 13.6 1:30.83 gnome-shell
7623 root 20 0 424852 82132 55152 S 3.0 4.4 0:28.00 X
13 root rt 0 0 0 0 S 0.3 0.0 0:00.07 migration/1
61 root 20 0 0 0 0 S 0.3 0.0 0:01.45 kworker/7:1
81 root 20 0 0 0 0 S 0.3 0.0 0:01.47 kworker/0:1
99 root 20 0 0 0 0 S 0.3 0.0 0:00.67 kworker/3:1
100 root 20 0 0 0 0 S 0.3 0.0 0:00.92 kworker/2:1
773 root 20 0 0 0 0 S 0.3 0.0 0:01.00 kworker/4:1
6347 root 20 0 90500 3164 2300 S 0.3 0.2 0:02.90 rngd
1 root 20 0 194216 6440 3340 S 0.0 0.3 0:03.61 systemd
2 root 20 0 0 0 0 S 0.0 0.0 0:00.02 kthreadd
3 root 20 0 0 0 0 S 0.0 0.0 0:00.37 ksoftirqd/0
5 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 kworker/0:0H
7 root rt 0 0 0 0 S 0.0 0.0 0:00.07 migration/0
8 root 20 0 0 0 0 S 0.0 0.0 0:00.00 rcu_bh
9 root 20 0 0 0 0 S 0.0 0.0 0:02.44 rcu_sched
10 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 lru-add-drain
上面执行结果中的
load average: 0.89, 0.64, 0.35
表示cpu 1分钟、5分钟、15分钟 使用率（%）
这时如果按一下键盘上的1，就会显示具体的各个核的cpu
top - 15:04:27 up 3:43, 3 users, load average: 1.71, 1.21, 0.65
Tasks: 260 total, 3 running, 257 sleeping, 0 stopped, 0 zombie
%Cpu0 : 12.5 us, 5.1 sy, 0.0 ni, 82.2 id, 0.3 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu1 : 8.1 us, 3.7 sy, 0.0 ni, 88.3 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu2 : 8.8 us, 10.1 sy, 0.0 ni, 81.1 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu3 : 4.4 us, 4.4 sy, 0.0 ni, 91.3 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu4 : 5.0 us, 7.0 sy, 0.0 ni, 88.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu5 : 7.0 us, 5.7 sy, 0.0 ni, 87.0 id, 0.3 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu6 : 5.0 us, 8.4 sy, 0.0 ni, 86.6 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
%Cpu7 : 4.0 us, 4.7 sy, 0.0 ni, 91.0 id, 0.0 wa, 0.0 hi, 0.3 si, 0.0 st
KiB Mem : 1863252 total, 113492 free, 913500 used, 836260 buff/cache
KiB Swap: 2097148 total, 2095100 free, 2048 used. 644060 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
16970 wsh 20 0 3244408 94828 12524 S 66.8 5.1 3:33.11 java
15799 wsh 20 0 771448 37568 20308 D 38.2 2.0 3:12.12 gnome-terminal-
13628 wsh 20 0 4244796 252828 69964 S 2.0 13.6 1:31.90 gnome-shell
7623 root 20 0 424852 82132 55152 S 1.7 4.4 0:28.76 X
35 root 20 0 0 0 0 R 0.3 0.0 0:10.50 kworker/5:0
60 root 20 0 0 0 0 S 0.3 0.0 0:01.98 kworker/6:1
61 root 20 0 0 0 0 S 0.3 0.0 0:02.19 kworker/7:1
81 root 20 0 0 0 0 S 0.3 0.0 0:01.86 kworker/0:1
100 root 20 0 0 0 0 S 0.3 0.0 0:01.64 kworker/2:1
773 root 20 0 0 0 0 S 0.3 0.0 0:01.80 kworker/4:1
3162 root 20 0 0 0 0 S 0.3 0.0 0:02.13 xfsaild/dm-0
6360 root 20 0 320324 5752 4256 S 0.3 0.3 0:16.30 vmtoolsd
uptime 命令
查看cpu 精简版命令
[wsh@localhost ~]$ uptime
15:06:58 up 3:46, 3 users, load average: 1.57, 1.39, 0.81
vmstat 可以查看cpu
一般vmstat工具的使用是通过两个数字参数来完成的，第一个参数是采样的时间间隔数单位是秒，第二个参数是采样的次数
procs
- r:运行和等待CPU时间片的进程数，原则上1核的CPU的运行队列不要超过2，整个系统的运行队列不能超过总核数的2倍，否则代表系统压力过大
- b:等待资源的进程数，比如正在等待磁盘I/o、网络I/o等。
cpu
- us:用户进程消耗CPUI时间百分比，us值高，用户进程消耗CPU时间多，如果长期大于50%，优化程序;
- sy:内核进程消耗的CPU时间百分比;
- us + sy参考值为80%，如果us + sy大于80%，说明可能存在CPU不足.
- id:处于空闲的CPU百分比.
- wa:系统等待IO的CPU时间百分比.
- st:来自于一个虚拟机偷取的CPU时间的百分比
[wsh@localhost ~]$ vmstat -n 2 3
procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
r b swpd free buff cache si so bi bo in cs us sy id wa st
3 0 2048 110012 36 835700 0 0 13 8 149 210 2 2 95 0 0
2 0 2048 109884 36 835744 0 0 0 74 3365 4975 6 7 87 0 0
1 0 2048 109692 36 835464 0 0 0 116 3337 4826 7 6 87 0 0
查看所有核的cpu信息 mpstat
# 每10s 采样一次
mpstat -P ALL 10
[wsh@localhost ~]$ mpstat -P ALL 10
Linux 3.10.0-957.el7.x86_64 (localhost.localdomain) 2021年05月15日 _x86_64_ (8 CPU)
18时16分55秒 CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle
18时16分57秒 all 6.29 0.00 6.29 0.13 0.00 0.06 0.00 0.00 0.00 87.24
18时16分57秒 0 9.64 0.00 3.05 0.00 0.00 0.51 0.00 0.00 0.00 86.80
18时16分57秒 1 4.55 0.00 3.03 0.00 0.00 0.00 0.00 0.00 0.00 92.42
18时16分57秒 2 4.04 0.00 10.10 0.00 0.00 0.00 0.00 0.00 0.00 85.86
18时16分57秒 3 2.51 0.00 5.03 0.00 0.00 0.00 0.00 0.00 0.00 92.46
18时16分57秒 4 13.71 0.00 7.11 0.51 0.00 0.00 0.00 0.00 0.00 78.68
18时16分57秒 5 9.55 0.00 3.52 0.50 0.00 0.00 0.00 0.00 0.00 86.43
18时16分57秒 6 3.52 0.00 10.55 0.00 0.00 0.00 0.00 0.00 0.00 85.93
18时16分57秒 7 2.51 0.00 7.04 0.00 0.00 0.00 0.00 0.00 0.00 90.45
每个进程使用cpu的用量分解信息
[wsh@localhost ~]$ ps -ef | grep java
wsh 16970 16881 63 14:58 pts/1 02:06:54 java JavaDemo
wsh 19532 16992 0 18:19 pts/0 00:00:00 grep --color=auto java
# pidstat -u 频率（s） -p 进程id
# 每10s钟采样一次
[wsh@localhost ~]$ pidstat -u 10 -p 16970
Linux 3.10.0-957.el7.x86_64 (localhost.localdomain) 2021年05月15日 _x86_64_ (8 CPU)
18时20分18秒 UID PID %usr %system %guest %CPU CPU Command
18时20分28秒 1000 16970 27.30 35.50 0.00 62.80 3 java
18时20分38秒 1000 16970 26.70 35.60 0.00 62.30 3 java
查看内存 free
# -m 指定显示的单位，m是兆
[wsh@localhost ~]$ free -m
total used free shared buff/cache available
Mem: 1819 908 100 59 810 612
Swap: 2047 2 2045
一般：
- 应用程序可用内存/系统物理内存>70%内存充足
- 应用程序可用内存/系统物理内存<20%内存不足，需要增加内存
- 20%<应用程庭可用内存/系统物理内存<70%内存基本够用
查看进程对内存的用量
[wsh@localhost ~]$ ps -ef | grep java
wsh 16970 16881 63 14:58 pts/1 02:12:23 java JavaDemo
wsh 19685 16992 0 18:28 pts/0 00:00:00 grep --color=auto java
# pidstat -p 进程id-r 采样频率
[wsh@localhost ~]$ pidstat -p 16970 -r 2
Linux 3.10.0-957.el7.x86_64 (localhost.localdomain) 2021年05月15日 _x86_64_ (8 CPU)
18时29分01秒 UID PID minflt/s majflt/s VSZ RSS %MEM Command
18时29分03秒 1000 16970 2.50 0.00 3244408 94900 5.09 java
18时29分05秒 1000 16970 4.50 0.00 3244408 94900 5.09 java
18时29分07秒 1000 16970 2.50 0.00 3244408 94900 5.09 java
查看硬盘 df
[wsh@localhost ~]$ df -h
文件系统 容量 已用 可用 已用% 挂载点
/dev/mapper/centos-root 15G 8.4G 6.7G 56% /
devtmpfs 894M 0 894M 0% /dev
tmpfs 910M 0 910M 0% /dev/shm
tmpfs 910M 11M 900M 2% /run
tmpfs 910M 0 910M 0% /sys/fs/cgroup
/dev/sda1 197M 157M 41M 80% /boot
tmpfs 182M 8.0K 182M 1% /run/user/42
tmpfs 182M 40K 182M 1% /run/user/1000
/dev/sr0 4.3G 4.3G 0 100% /run/media/wsh/CentOS 7 x86_64
查看磁盘IO
# 每2s采样一次，共采样3次
[wsh@localhost ~]$ iostat -xdk 2 3
Linux 3.10.0-957.el7.x86_64 (localhost.localdomain) 2021年05月15日 _x86_64_ (8 CPU)
Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await r_await w_await svctm %util
sda 0.01 0.07 1.14 4.55 78.65 78.22 55.18 0.03 4.78 9.87 3.50 1.82 1.04
scd0 0.00 0.00 0.00 0.00 0.04 0.00 72.41 0.00 13.79 13.79 0.00 13.28 0.00
dm-0 0.00 0.00 1.06 4.52 77.36 78.08 55.64 0.04 6.89 10.53 6.03 1.85 1.03
dm-1 0.00 0.00 0.01 0.01 0.11 0.06 16.07 0.00 8.10 3.22 10.37 0.81 0.00
Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await r_await w_await svctm %util
sda 0.00 0.00 0.50 7.00 4.00 84.00 23.47 0.01 1.13 0.00 1.21 1.13 0.85
scd0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
dm-0 0.00 0.00 0.50 7.00 4.00 84.00 23.47 0.01 1.13 0.00 1.21 1.13 0.85
dm-1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await r_await w_await svctm %util
sda 0.00 0.00 0.00 7.46 0.00 101.49 27.20 0.02 2.33 0.00 2.33 2.33 1.74
scd0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
dm-0 0.00 0.00 0.00 7.46 0.00 101.49 27.20 0.02 2.33 0.00 2.33 2.33 1.74
dm-1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
磁盘块设备分布
- rkB/s每秒读取数据量kB;
- wkB/s每秒写入数据量kB;
- svctm l/O请求的平均服务时间，单位毫秒;
- await l/O请求的平均等待时间，单位毫秒;值越小，性能越好;
- util一秒中有百分几的时间用于I/O操作。接近100%时，表示磁盘带宽跑满，需要优化程序或者增加磁盘;
- rkB/s、wkB/s根据系统应用不同会有不同的值，但有规律遵循:长期、超大数据读写，肯定不正常，需要优化程序读取。svctm的值与await的值很接近，表示几乎没有Io等待，磁盘性能好，
如果await的值远高于svctm的值，则表示IO队列等待太长，需要优化程序或更换更快磁盘。
查看对应进程的磁盘IO读写情况
[wsh@localhost ~]$ ps -ef | grep java
wsh 16970 16881 63 14:58 pts/1 02:17:19 java JavaDemo
wsh 19829 16992 0 18:36 pts/0 00:00:00 grep --color=auto java
# pidstat -d 采样频率 -p 进程id
[wsh@localhost ~]$ pidstat -d 2 -p 16970
Linux 3.10.0-957.el7.x86_64 (localhost.localdomain) 2021年05月15日 _x86_64_ (8 CPU)
18时37分02秒 UID PID kB_rd/s kB_wr/s kB_ccwr/s Command
18时37分04秒 1000 16970 0.00 0.00 0.00 java
18时37分06秒 1000 16970 0.00 8.00 0.00 java
18时37分08秒 1000 16970 0.00 0.00 0.00 java
查看网络IO
# 每两秒采样一次
ifstat 2
需要安装的话，安装命令为：
[wsh@localhost ~]$ wget http://gael.roualland.free.fr/ifstat/ifstat-1.1.tar.gz
[wsh@localhost ~]$ tar zxvf ifstat-1.1.tar.gz
[wsh@localhost ~]$ cd ifstat-1.1/
[wsh@localhost ifstat-1.1]$ ./configure
[wsh@localhost ifstat-1.1]$ make
[wsh@localhost ifstat-1.1]$ make install
如何排除占用cpu过高的程序
1. 整体查看top
top - 18:55:41 up 7:35, 3 users, load average: 1.69, 1.73, 1.71
Tasks: 257 total, 3 running, 254 sleeping, 0 stopped, 0 zombie
%Cpu(s): 6.5 us, 6.5 sy, 0.0 ni, 86.8 id, 0.1 wa, 0.0 hi, 0.0 si, 0.0 st
KiB Mem : 1863252 total, 88248 free, 931280 used, 843724 buff/cache
KiB Swap: 2097148 total, 2095100 free, 2048 used. 626508 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
16970 wsh 20 0 3244408 94900 12528 S 62.3 5.1 149:11.35 java
15799 wsh 20 0 773848 39540 20576 R 39.7 2.1 91:57.92 gnome-terminal-
13628 wsh 20 0 4260820 263544 64620 S 3.6 14.1 2:43.74 gnome-shell
7623 root 20 0 425156 82396 55416 R 3.3 4.4 1:03.59 X
13646 wsh 9 -11 1285512 6844 3976 S 0.7 0.4 0:01.48 pulseaudio
61 root 20 0 0 0 0 S 0.3 0.0 0:40.08 kworker/7:1
81 root 20 0 0 0 0 S 0.3 0.0 0:23.10 kworker/0:1
13854 wsh 20 0 779864 14664 9480 S 0.3 0.8 0:02.76 gsd-color
17768 root 20 0 0 0 0 S 0.3 0.0 0:33.13 kworker/6:2
19382 root 20 0 0 0 0 S 0.3 0.0 0:07.71 kworker/2:2
20775 root 20 0 0 0 0 S 0.3 0.0 0:00.80 kworker/1:0
1 root 20 0 194216 6440 3340 S 0.0 0.3 0:04.26 systemd
2 root 20 0 0 0 0 S 0.0 0.0 0:00.04 kthreadd
3 root 20 0 0 0 0 S 0.0 0.0 0:00.47 ksoftirqd/0
5 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 kworker/0:0H
7 root rt 0 0 0 0 S 0.0 0.0 0:03.17 migration/0
8 root 20 0 0 0 0 S 0.0 0.0 0:00.00 rcu_bh
9 root 20 0 0 0 0 S 0.0 0.0 0:14.39 rcu_sched
10 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 lru-add-drain
从上面可以看出进程id为 16970 java程序占用cpu过高
16970 wsh 20 0 3244408 94900 12528 S 62.3 5.1 149:11.35 java
也可以详细查看单个进程的top情况：
# top -Hp 进程id
[wsh@localhost ~]$ top -Hp 16970
top - 18:58:07 up 7:37, 3 users, load average: 1.72, 1.76, 1.72
Threads: 20 total, 1 running, 19 sleeping, 0 stopped, 0 zombie
%Cpu(s): 6.5 us, 6.2 sy, 0.0 ni, 86.9 id, 0.2 wa, 0.0 hi, 0.1 si, 0.0 st
KiB Mem : 1863252 total, 88680 free, 931328 used, 843244 buff/cache
KiB Swap: 2097148 total, 2095100 free, 2048 used. 626312 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
16971 wsh 20 0 3244408 94900 12528 R 59.7 5.1 145:56.30 java
16972 wsh 20 0 3244408 94900 12528 S 0.3 5.1 0:32.92 java
16974 wsh 20 0 3244408 94900 12528 S 0.3 5.1 0:32.99 java
16976 wsh 20 0 3244408 94900 12528 S 0.3 5.1 0:32.12 java
16978 wsh 20 0 3244408 94900 12528 S 0.3 5.1 0:32.64 java
16970 wsh 20 0 3244408 94900 12528 S 0.0 5.1 0:00.00 java
16973 wsh 20 0 3244408 94900 12528 S 0.0 5.1 0:32.60 java
16975 wsh 20 0 3244408 94900 12528 S 0.0 5.1 0:32.40 java
16977 wsh 20 0 3244408 94900 12528 S 0.0 5.1 0:32.83 java
16979 wsh 20 0 3244408 94900 12528 S 0.0 5.1 0:32.54 java
16980 wsh 20 0 3244408 94900 12528 S 0.0 5.1 0:14.71 VM Thread
16981 wsh 20 0 3244408 94900 12528 S 0.0 5.1 0:00.00 Reference Handl
16982 wsh 20 0 3244408 94900 12528 S 0.0 5.1 0:00.00 Finalizer
2. 查看进程中占用cpu过高的线程id
# ps -mp 进程id -o THREAD,tid,time
[wsh@localhost ~]$ ps -mp 16970 -o THREAD,tid,time
USER %CPU PRI SCNT WCHAN USER SYSTEM TID TIME
wsh 62.9 - - - - - - 02:31:36
wsh 0.0 19 - futex_ - - 16970 00:00:00
wsh 60.9 19 - n_tty_ - - 16971 02:26:48
wsh 0.2 19 - futex_ - - 16972 00:00:33
wsh 0.2 19 - futex_ - - 16973 00:00:32
wsh 0.2 19 - futex_ - - 16974 00:00:33
wsh 0.2 19 - futex_ - - 16975 00:00:32
wsh 0.2 19 - futex_ - - 16976 00:00:32
wsh 0.2 19 - futex_ - - 16977 00:00:33
wsh 0.2 19 - futex_ - - 16978 00:00:32
wsh 0.2 19 - futex_ - - 16979 00:00:32
wsh 0.1 19 - futex_ - - 16980 00:00:14
wsh 0.0 19 - futex_ - - 16981 00:00:00
wsh 0.0 19 - futex_ - - 16982 00:00:00
wsh 0.0 19 - futex_ - - 16983 00:00:00
wsh 0.0 19 - futex_ - - 16984 00:00:00
wsh 0.0 19 - futex_ - - 16985 00:00:00
wsh 0.0 19 - futex_ - - 16986 00:00:00
wsh 0.0 19 - futex_ - - 16987 00:00:00
wsh 0.0 19 - futex_ - - 16988 00:00:00
wsh 0.0 19 - futex_ - - 16989 00:00:09
发现 16971 这个线程id占用cpu过高：
wsh 60.9 19 - n_tty_ - - 16971 02:26:48
3. 将线程id转化成16进制
# 将线程号转化成16进制
# printf "%x\n" <线程的pid>
[wsh@localhost ~]$ printf "%x\n" 16971
424b
4. 使用jdk提供的命令来找出具体代码造成的cpu过高问题
# jstack 进程id | grep 线程id的16进制数（小写） -A60
[wsh@localhost ~]$ jstack 16970 | grep 424b -A60
"main" #1 prio=5 os_prio=0 tid=0x00007fb2e804b800 nid=0x424b runnable [0x00007fb2f089d000]
java.lang.Thread.State: RUNNABLE
at java.io.FileOutputStream.writeBytes(Native Method)
at java.io.FileOutputStream.write(FileOutputStream.java:326)
at java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:82)
at java.io.BufferedOutputStream.flush(BufferedOutputStream.java:140)
- locked <0x00000000e3805d38> (a java.io.BufferedOutputStream)
at java.io.PrintStream.write(PrintStream.java:482)
- locked <0x00000000e3805170> (a java.io.PrintStream)
at sun.nio.cs.StreamEncoder.writeBytes(StreamEncoder.java:221)
at sun.nio.cs.StreamEncoder.implFlushBuffer(StreamEncoder.java:291)
at sun.nio.cs.StreamEncoder.flushBuffer(StreamEncoder.java:104)
- locked <0x00000000e3805128> (a java.io.OutputStreamWriter)
at java.io.OutputStreamWriter.flushBuffer(OutputStreamWriter.java:185)
at java.io.PrintStream.newLine(PrintStream.java:546)
- eliminated <0x00000000e3805170> (a java.io.PrintStream)
at java.io.PrintStream.println(PrintStream.java:737)
- locked <0x00000000e3805170> (a java.io.PrintStream)
at JavaDemo.main(JavaDemo.java:8)
"VM Thread" os_prio=0 tid=0x00007fb2e80df000 nid=0x4254 runnable
"GC task thread#0 (ParallelGC)" os_prio=0 tid=0x00007fb2e805e000 nid=0x424c runnable
"GC task thread#1 (ParallelGC)" os_prio=0 tid=0x00007fb2e8060000 nid=0x424d runnable
"GC task thread#2 (ParallelGC)" os_prio=0 tid=0x00007fb2e8062000 nid=0x424e runnable
"GC task thread#3 (ParallelGC)" os_prio=0 tid=0x00007fb2e8063800 nid=0x424f runnable
"GC task thread#4 (ParallelGC)" os_prio=0 tid=0x00007fb2e8065800 nid=0x4250 runnable
"GC task thread#5 (ParallelGC)" os_prio=0 tid=0x00007fb2e8067800 nid=0x4251 runnable
"GC task thread#6 (ParallelGC)" os_prio=0 tid=0x00007fb2e8069800 nid=0x4252 runnable
"GC task thread#7 (ParallelGC)" os_prio=0 tid=0x00007fb2e806b000 nid=0x4253 runnable
"VM Periodic Task Thread" os_prio=0 tid=0x00007fb2e813c000 nid=0x425d waiting on condition
JNI global references: 5
从上面可以看出：
at JavaDemo.main(JavaDemo.java:8)