使用systemd 指令碼設定服務keepalive

systemd是linux下的一種init軟體，由lennart poettering帶頭開發，其開發目標是提供更優秀的框架以表示系統服務間的依賴關係，並依此實現系統初始化時服務的並行啟動，同時達到降低shell的系統開銷的效果，最終代替現在常用的system v與bsd風格init程式。傳統sysvinit使用inittab來決定執行哪些shell指令碼，大量使用shell指令碼被認為是效率低下無法並行的原因。systemd使用了linux專屬技術，不再顧及posix相容.

配置檔案目錄: /etc/systemd/system/

vim /etc/systemd/system/binlogdata_to_kafka_test.service

[unit]
description=maxwell binlogdata_to_kafka_test
wants=network-online.target
after=network-online.target
[service]
type=******
execstart=/data/maxwell/bin/maxwell --config /data/maxwell/binlogdata_to_kafka_test.properties
workingdirectory=/data/maxwell/
standardoutput=inherit
standarderror=inherit
restart=always
restartsec=20
user=hdfs
startlimitintervalsec=0
[install]
wantedby=multi-user.target

重要引數說明:

①: startlimitintervalsec: 設定單元的啟動頻率限制。 startlimitintervalsec= 用於設定時長，預設值等於 defaultstartlimitintervalsec= 的值(預設為10秒)，設為 0 表示不作限制。

②: 如果要以90秒的間隔, 重新啟動服務3次, 可以在systemd服務檔案的section塊[service]中包含以下行：

restart=always

restartsec=90

startlimitinterval=300

startlimitburst=3

注意: 請注意,』startlimitinterval』必須大於』restartsec * startlimitburst』,否則服務將無限期地重新啟動.

systemctl daemon-reload

systemctl [ enable | disable | is-enabled | is-active ] ***x.service

systemctl [ start | stop | restart ] ***x.service

systemctl status ***x.service

systemctl list-units --type=service

[root@cdh1 system]# systemctl list-units --type=service unit load active sub description atd.service loaded active running job spooling tools auditd.service loaded active running security auditing service cloud-final.service loaded active exited execute cloud user/final scripts cloud-init-local.service loaded active exited initial cloud-init job (pre-networking) cloud-init.service loaded active exited initial cloud-init job (metadata service c cloudera-scm-agent.service loaded active exited lsb: cloudera scm agent crond.service loaded active running command scheduler dbus.service loaded active running d-bus system message bus [email protected] loaded active running getty on tty1 ● hssinstall.service not-found active exited hssinstall.service irqbalance.service loaded active running irqbalance daemon kdump.service loaded active exited crash recovery kernel arming kmod-static-nodes.service loaded active exited create list of required static device node binlogdata_to_kafka_test.service loaded active running maxwell binlogdata_to_kafka_test load = reflects whether the unit definition was properly loaded. active = the high-level unit activation state, i.e. generalization of sub. sub = the low-level unit activation state, values depend on unit type. 17 loaded units listed. pass --all to see loaded but inactive units, too. to show all installed unit files use 'systemctl list-unit-files'.

在 /usr/lib/systemd/system/下面

enable命令是在/etc/systemd/system/multi-user.target.wants 下做的指向unit目錄的(一般為/usr/lib/systemd/system/, 也可以在/etc/systemd/system/下)軟鏈結,如下:

[root@cdh1 multi-user.target.wants]# ll total 0 lrwxrwxrwx. 1 root root 35 feb 27 2019 atd.service -> /usr/lib/systemd/system/atd.service lrwxrwxrwx. 1 root root 38 feb 27 2019 auditd.service -> /usr/lib/systemd/system/auditd.service lrwxrwxrwx 1 root root 58 dec 21 13:47 binlogdata_to_kafka_test.service -> /etc/systemd/system/binlogdata_to_kafka_test.service

如果修改了配置檔案，但未進行過載的話，每次啟動、重啟都會爆出警告，類似如下：

[root@cdh01 system]# systemctl status bigdata_test_sh

。。。warning: bigdata_test_sh.service changed on disk. run 『systemctl daemon-reload』 to reload units.

因此，每次修改完畢配置檔案，都需要使用該命令進行配置檔案過載操作：

使用systemd 指令碼設定服務keepalive

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