背景：有时候我们使用systemctl命令，如简单点的systemctl start memcached来讲，出现错时，会有一些提示，但是提示的内容是变量，其并没有将参数给编译后的值放入，于是出现如下所示，但是要失败了怎么排查这些参数呢？此文就讲这个问题，如果不是为了linux开机启动提速而并行启动外，这个systemctl其本质是想接管很多东西，但也带来了很多麻烦，难怪linus对此有一定的意见，系统要保持简单，好用。像开机慢可以少开机或不关机嘛，学学人家苹果升级在半夜，你慢就慢，谁管你，从策略上就规避了，把技术搞复杂还是简单是一门哲学，而创始人的价值就在于坚守设计艺术，而不光是技术。
● memcached.service - Memcached
Loaded: loaded (/usr/lib/systemd/system/memcached.service; enabled; vendor preset: disabled)
Active: inactive (dead) since Fri 2018-07-20 18:48:50 CST; 19h ago
Process: 15266 ExecStart=/usr/local/memcached/bin/memcached -u $USER -p $PORT -m $CACHESIZE -c $MAXCONN $OPTIONS (code=exited, status=0/SUCCESS)
Main PID: 15266 (code=exited, status=0/SUCCESS)
失败：
systemctl start memcached
Job for memcached.service failed because the control process exited with error code. See "systemctl status memcached.service" and "journalctl -xe" for details.
[Unit]
Description=Memcached
Before=httpd.service
After=network.target
[Service]
Type=simple
ExecStartPre=/bin/bash -l -c 'echo "/usr/local/memcached/bin/memcached" -u $USER -p $PORT -m $CACHESIZE -c $MAXC
ONN $OPTIONS > /tmp/systemctl.debug'
EnvironmentFile=-/etc/sysconfig/memcached
ExecStart=/usr/local/memcached/bin/memcached -u $USER -p $PORT -m $CACHESIZE -c $MAXCONN $OPTIONS
[Install]
WantedBy=multi-user.target
/etc/sysconfig/memcached
PORT="11211"
systemctl daemon-reload
systemctl start memcached
systemctl status memcached.service
Active: failed (Result: exit-code) since Sat 2018-07-21 14:35:22 CST; 5s ago
Process: 11417 ExecStart=/usr/local/memcached/bin/memcached -u $USER -p $PORT -m $CACHESIZE -c $MAXCONN $OPTIONS (code=exited, status=71)
Process: 11399 ExecStartPre=/bin/bash -l -c echo "/usr/local/memcached/bin/memcached" -u $USER -p $PORT -m $CACHESIZE -c $MAXCONN $OPTIONS > /tmp/systemctl.debug (code=exited, status=0/SUCCESS)
Main PID: 11417 (code=exited, status=71)
如果有错，需要挑食的参数查看 /tmp/systemctl.debug：
cat /tmp/systemctl.debug
/usr/local/memcached/bin/memcached -u root -p 11211 -m 64 -c 1024 -vv >> /data/logs/memcached/11211/memcached.log 2>&1