systemd 看 log, 還有 service 的 echo output

ref:Ultimate Guide to Logging

systemd 啟動得 service，值行的 script，其中有 echo 的，都 echo 到 journald 裡。
所以要把 journald 打開。

/etc/systemd/journald.conf

其中，第一個 config option:

[Journal]
Storage=auto
...

可以選...

• “none” :
  This effectively turns off journaling. Any log message received will be dropped. However, any redirection to console, syslog, or kernel log buffer would still be in effect.
• “volatile” :
  Journal data is saved in memory and temporarily available under the /run/log/journal directory. The directory will be created if it does not exist.
• “persistent” :
  Journal data is saved persistently on disk under the /var/log/journal directory. The directory will be created if it does not exist. If the disk volume is not accessible or writable, the files will be created under /run/log/journal.
• “auto” :
  The storage mode is like persistent—data will be written to disk; however, if the /var/log/journal directory does not exist, it will be created under /run/log/journal.

journald 存的是壓縮檔(?)，所以不能直接 cat，要用journalctl 來看..