docker里用top的一个坑

业务背景

使用 top + grep 来判断一个进程是否退出。如果grep不到了，就说明退出里，否则等待1秒钟重新判断

测试进程process_abc，sleep 5秒钟后自动退出

#include <stdio.h>

int main()
{
        sleep(5);
        return 0;
}

检测脚本

velscode@velscode:~/test$ cat check.sh
#/bin/bash

while true
do
        top -n 1 -b | grep "process_abc"
        if [ $? -eq 0 ];then
                echo "process_abc alive, wait it"
                sleep 1
        else
                echo "process_abc exit"
                break
        fi
done

问题现象

通过 docker run --it .. 进入容器bash，手工执行命令，正常

检测脚本检测到目标进程5次，每次等待1秒，process_abc退出后，执行结束

# 拉起容器的脚本
velscode@velscode:~/test$ cat run_manual.sh
DOCKER_CONTAINER_TAG=ubuntu/test:1.0

docker build -f Dockerfile . -t ${DOCKER_CONTAINER_TAG}
docker run -it --privileged \
 -v $(pwd):/opt/ \
 -w /opt/ \
 ${DOCKER_CONTAINER_TAG} /bin/bash

# 拉起容器
velscode@velscode:~/test$ bash run_manual.sh
Sending build context to Docker daemon  24.58kB
Step 1/1 : FROM ubuntu:latest
 ---> ba6acccedd29
Successfully built ba6acccedd29
Successfully tagged ubuntu/test:1.0

# 执行测试进程和检测脚本
root@a63946704302:/opt# ./process_abc & bash check.sh
[1] 9
     9 root      20   0    2352    516    452 S   0.0   0.1   0:00.00 process_abc
process_abc alive, wait it
     9 root      20   0    2352    516    452 S   0.0   0.1   0:00.00 process_abc
process_abc alive, wait it
     9 root      20   0    2352    516    452 S   0.0   0.1   0:00.00 process_abc
process_abc alive, wait it
     9 root      20   0    2352    516    452 S   0.0   0.1   0:00.00 process_abc
process_abc alive, wait it
     9 root      20   0    2352    516    452 S   0.0   0.1   0:00.00 process_abc
process_abc alive, wait it
process_abc exit
[1]+  Done                    ./process_abc

如果采用 docker run ... /bin/bash -c "./process_abc & bash check.sh"，则检测脚本无法检测到进程

# 拉起容器的脚本
velscode@velscode:~/test$ cat run_docker.sh
DOCKER_CONTAINER_TAG=ubuntu/test:1.0

docker build -f Dockerfile . -t ${DOCKER_CONTAINER_TAG}
docker run --privileged \
 -v $(pwd):/opt/ \
 -w /opt/ \
 ${DOCKER_CONTAINER_TAG} /bin/bash -c "export TERM=xterm; ./process_abc & bash check.sh"

# 执行结果
velscode@velscode:~/test$ bash run_docker.sh
Sending build context to Docker daemon  24.58kB
Step 1/1 : FROM ubuntu:latest
 ---> ba6acccedd29
Successfully built ba6acccedd29
Successfully tagged ubuntu/test:1.0
process_abc exit

问题原因

在docker中，终端默认宽度比较小，top结果的进程名显示不全

velscode@velscode:~/test$ cat run_docker.sh
DOCKER_CONTAINER_TAG=ubuntu/test:1.0
docker build -f Dockerfile . -t ${DOCKER_CONTAINER_TAG}
docker run --privileged \
 -v $(pwd):/opt/ \
 -w /opt/ \
 ${DOCKER_CONTAINER_TAG} /bin/bash -c "export TERM=xterm; ./process_abc & top -n 1 -b"


velscode@velscode:~/test$ bash run_docker.sh
Sending build context to Docker daemon  24.58kB
Step 1/1 : FROM ubuntu:latest
 ---> ba6acccedd29
Successfully built ba6acccedd29
Successfully tagged ubuntu/test:1.0
top - 11:06:12 up  1:39,  0 users,  load average: 0.01, 0.08, 0.08
Tasks:   3 total,   1 running,   2 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.0 us,  0.0 sy,  0.0 ni, 93.3 id,  6.7 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :    962.1 total,    119.1 free,    256.5 used,    586.6 buff/cache
MiB Swap:   1924.0 total,   1922.5 free,      1.5 used.    551.5 avail Mem

   PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
     1 root      20   0    3980   2952   2740 S   0.0   0.3   0:00.00 bash
     7 root      20   0    2352    576    516 S   0.0   0.1   0:00.00 process_+
     8 root      20   0    5972   3204   2776 R   0.0   0.3   0:00.00 top

导致grep失败。

解决方法

使用 top 的 w参数指定宽度

velscode@velscode:~/test$ cat run_docker.sh
DOCKER_CONTAINER_TAG=ubuntu/test:1.0
docker build -f Dockerfile . -t ${DOCKER_CONTAINER_TAG}
docker run --privileged \
 -v $(pwd):/opt/ \
 -w /opt/ \
 ${DOCKER_CONTAINER_TAG} /bin/bash -c "export TERM=xterm; ./process_abc & top -n 1 -b -w 512"


velscode@velscode:~/test$ bash run_docker.sh
Sending build context to Docker daemon  25.09kB
Step 1/1 : FROM ubuntu:latest
 ---> ba6acccedd29
Successfully built ba6acccedd29
Successfully tagged ubuntu/test:1.0
top - 11:07:57 up  1:40,  0 users,  load average: 0.07, 0.07, 0.08
Tasks:   3 total,   1 running,   2 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.0 us,  0.0 sy,  0.0 ni, 93.3 id,  6.7 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :    962.1 total,    115.5 free,    258.3 used,    588.4 buff/cache
MiB Swap:   1924.0 total,   1922.5 free,      1.5 used.    549.6 avail Mem

   PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
     1 root      20   0    3980   2944   2728 S   0.0   0.3   0:00.00 bash
     7 root      20   0    2352    584    520 S   0.0   0.1   0:00.00 process_abc
     8 root      20   0    5972   3232   2808 R   0.0   0.3   0:00.00 top

可以看到进程名显示全了，grep可以正常工作里