考虑来自该 journalctl 输出的以下三个条目（为完整性打开 json 输出和调试模式）：
SYSTEMD_LOG_LEVEL=debug journalctl -o json -u docker --since '1 hour ago'
Root directory /run/log/journal added.
Considering /run/log/journal/de1e08ac57af453bacab3cc9875b12b9.
Directory /run/log/journal/de1e08ac57af453bacab3cc9875b12b9 added.
File /run/log/journal/de1e08ac57af453bacab3cc9875b12b9/system.journal added.
File /run/log/journal/de1e08ac57af453bacab3cc9875b12b9/system@7bea274da69540c8b1676a1cd030f6ee-0000000001022a21-00054cd4f00adc68.journal added.
File /run/log/journal/de1e08ac57af453bacab3cc9875b12b9/system@7bea274da69540c8b1676a1cd030f6ee-000000000101fcf0-00054cd199b0289f.journal added.
File /run/log/journal/de1e08ac57af453bacab3cc9875b12b9/system@7bea274da69540c8b1676a1cd030f6ee-000000000101cd35-00054ccd960f91a8.journal added.
File /run/log/journal/de1e08ac57af453bacab3cc9875b12b9/system@7bea274da69540c8b1676a1cd030f6ee-0000000001019c1d-00054ccab4dac8d5.journal added.
File /run/log/journal/de1e08ac57af453bacab3cc9875b12b9/system@7bea274da69540c8b1676a1cd030f6ee-0000000001016ae3-00054cc7d76493eb.journal added.
File /run/log/journal/de1e08ac57af453bacab3cc9875b12b9/system@7bea274da69540c8b1676a1cd030f6ee-00000000010139aa-00054cc4212faa29.journal added.
File /run/log/journal/de1e08ac57af453bacab3cc9875b12b9/system@7bea274da69540c8b1676a1cd030f6ee-0000000001010d45-00054cbe6893a794.journal added.
Considering /run/log/journal/c811c8a6e38845669ba5607794d4b425.
Directory /run/log/journal/c811c8a6e38845669ba5607794d4b425 added.
File /run/log/journal/c811c8a6e38845669ba5607794d4b425/system.journal added.
Journal filter: ((OBJECT_SYSTEMD_UNIT=docker.service AND _UID=0) OR (UNIT=docker.service AND _PID=1) OR (COREDUMP_UNIT=docker.service AND _UID=0 AND MESSAGE_ID=fc2e22bc6ee647b6b90729ab34a250b1) OR _SYSTEMD_UNIT=docker.service)
{ "__CURSOR" : "s=7bea274da69540c8b1676a1cd030f6ee;i=10260ef;b=15e9d32e03844e279dc0fcce7cb3c223;m=77b2f462910;t=54cd75d2cca7e;x=c30fbcda999df142", "__REALTIME_TIMESTAMP" : "1491862748449406", …