用Supervisor实现进程守护，在异常退出时自动重启

程序启动后，有些是以daemon的形式运行，但在意外退出后，如果不能及时重新启动，会有比较严重的影响。

比如Zimg在图片处理中由于某些图片处理失败，会导致zimg进程挂掉，影响正常的服务提供，并且只能在服务失效后才能察觉到。必须采用一个进程守护来时刻保证zimg进程挂掉后，再自动重新启动。本篇介绍Supervisor工具来进行Zimg进程的守护。

Supervisor是用Python开发的一套通用的进程管理程序，能将一个普通的命令行进程变为后台daemon，并监控进程状态，异常退出时能自动重启。

安装过程如下：

[root@localhost ~]# pip3 install supervisor
Collecting supervisor
Using cached https://files.pythonhosted.org/packages/44/60/698e54b4a4a9b956b2d709b4b7b676119c833d811d53ee2500f1b5e96dc3/supervisor-3.3.4.tar.gz
Complete output from command python setup.py egg_info:
Supervisor requires Python 2.4 or later but does not work on any version of Python 3. You are using version 3.5.2 (default, Jan 9 2017, 16:42:56)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-11)]. Please install using a supported version.
----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-build-15pcy5f3/supervisor/
You are using pip version 8.1.1, however version 18.0 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.

提示显示，python 3版本下，没办法正常安装Supervisor，只能先将python 3删除掉，再安装Supervisor。采用rm -rf xxxxx命令删除即可。

[root@localhost ~]# whereis python
python: /usr/bin/python /usr/bin/python2.7 /usr/bin/python2.7-config /usr/lib/python2.7 /usr/lib64/python2.7 /etc/python /usr/local/bin/python3.5m /usr/local/bin/python3.5 /usr/local/bin/python3.5m-config /usr/local/bin/python3.5-config /usr/local/lib/python3.5 /usr/include/python2.7 /usr/share/man/man1/python.1.gz

删除后，继续采用pip命令来安装Supervisor。

[root@wfm ~]# yum -y install pip
Loaded plugins: fastestmirror, refresh-packagekit, security
Loading mirror speeds from cached hostfile
* base: mirrors.tuna.tsinghua.edu.cn
* extras: mirrors.tuna.tsinghua.edu.cn
* updates: mirrors.tuna.tsinghua.edu.cn
Setting up Install Process
No package pip available.
Error: Nothing to do

解决方法：需要先安装扩展源EPEL。

EPEL(http://fedoraproject.org/wiki/EPEL) 是由 Fedora 社区打造，为 RHEL 及衍生发行版如 CentOS、Scientific Linux 等提供高质量软件包的项目。

首先安装epel扩展源：

yum -y install epel-release

然后再安装pip

yum -y install python-pip --安装成功后，简单测试下pip命令是否生效 [root@localhost bin]# pip -V pip 8.1.2 from /usr/lib/python2.7/site-packages (python 2.7)

[root@localhost bin]# pip install supervisor
Collecting supervisor
Using cached https://files.pythonhosted.org/packages/44/60/698e54b4a4a9b956b2d709b4b7b676119c833d811d53ee2500f1b5e96dc3/supervisor-3.3.4.tar.gz
Collecting meld3>=0.6.5 (from supervisor)
Downloading https://files.pythonhosted.org/packages/b6/ae/e6d731e4b9661642c1b20591d8054855bb5b8281cbfa18f561c2edd783f7/meld3-1.0.2-py2.py3-none-any.whl
Installing collected packages: meld3, supervisor
Running setup.py install for supervisor ... done
Successfully installed meld3-1.0.2 supervisor-3.3.4
You are using pip version 8.1.2, however version 18.0 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.