是否可以更改 systemd 托管服务用于日志记录的标签？例如，我的自定义服务report-daemon.service定义为
# ...
[Service]
ExecStart=/usr/bin/php # ...
# ...
显示为php而不是report-daemon（它似乎从 推断出标签ExecStart）
$ sudo journalctl --unit report-daemon
# ...
May 30 16:26:11 delta php[994]: Found 0 new revisions for Ctytn4a6zjw
May 30 16:26:12 delta php[994]: Found 0 new revisions for efE8xuvUjAo
# ...
手册页未列出在单元文件中设置此项的任何选项。是否可以在某处更改标签？
答案1
更新 1：详细选项将以长格式列出，因此包括 UNIT：
[root@localhost]# journalctl --unit newnginx -o verbose
-- Logs begin at Sun 2015-04-05 10:36:30 BST, end at Mon 2015-06-01 08:17:58 BST. --
Sun 2015-05-31 10:27:38.344553 BST [s=4cc44a9cf9344c948fd4716fe024439e;i=3198;b=be3381af5b1d4743a4ccc1e346eab405;m=1548bfaf08;t=5175d51fadf41;x=eb6bb8ee2b2be47e]
PRIORITY=6
_UID=0
_GID=0
_BOOT_ID=be3381af5b1d4743a4ccc1e346eab405
_MACHINE_ID=9619293167aa4f76b45b745e9f4e8935
_HOSTNAME=localhost.localdomain
_CAP_EFFECTIVE=1fffffffff
_SYSTEMD_CGROUP=/
SYSLOG_FACILITY=3
SYSLOG_IDENTIFIER=systemd
_TRANSPORT=journal
_PID=1
_COMM=systemd
_EXE=/usr/lib/systemd/systemd
_CMDLINE=/usr/lib/systemd/systemd --system --deserialize 21
_SELINUX_CONTEXT=system_u:system_r:init_t:s0
CODE_FILE=src/core/unit.c
CODE_LINE=1115
CODE_FUNCTION=unit_status_log_starting_stopping_reloading
MESSAGE_ID=7d4958e842da4a758f6c1cdc7b36dcc5
MESSAGE=Starting nginx - high performance web server...
UNIT=newnginx.service
_SOURCE_REALTIME_TIMESTAMP=1433064458344553
Sun 2015-05-31 10:27:38.354983 BST [s=4cc44a9cf9344c948fd4716fe024439e;i=3199;b=be3381af5b1d4743a4ccc1e346eab405;m=1548bfd0ee;t=5175d51fb0127;x=bc50f03db39f8d09]
PRIORITY=6
_UID=0
_GID=0
_BOOT_ID=be3381af5b1d4743a4ccc1e346eab405
_MACHINE_ID=9619293167aa4f76b45b745e9f4e8935
_HOSTNAME=localhost.localdomain
_CAP_EFFECTIVE=1fffffffff
_SYSTEMD_CGROUP=/
SYSLOG_FACILITY=3
_SELINUX_CONTEXT=system_u:system_r:init_t:s0
_TRANSPORT=stdout
更新 2：用于打印所需条目的 Python 脚本：
from systemd import journal
j = journal.Reader()
j.this_boot()
j.add_match(_SYSTEMD_UNIT="newnginx.service")
for entry in j:
print('{} {}'.format(entry['_SYSTEMD_UNIT'], entry['MESSAGE']))
看一下 nginx 的这个例子：
[root@localhost tmp]# journalctl --unit nginx
-- Logs begin at Sun 2015-04-05 10:36:30 BST, end at Sun 2015-05-31 11:12:29 BST. --
May 31 10:20:41 localhost.localdomain systemd[1]: Starting nginx - high performance web server...
May 31 10:20:41 localhost.localdomain nginx[111169]: nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
May 31 10:20:41 localhost.localdomain nginx[111169]: nginx: configuration file /etc/nginx/nginx.conf test is successful
May 31 10:20:41 localhost.localdomain systemd[1]: Failed to read PID from file /run/nginx.pid: Invalid argument
May 31 10:20:41 localhost.localdomain systemd[1]: Started nginx - high performance web server.
May 31 10:27:05 localhost.localdomain systemd[1]: Stopping nginx - high performance web server...
May 31 10:27:05 localhost.localdomain systemd[1]: Stopped nginx - high performance web server.
May 31 10:58:36 localhost.localdomain systemd[1]: Stopped nginx - high performance web server.
May 31 11:12:29 localhost.localdomain systemd[1]: Starting nginx - high performance web server...
May 31 11:12:29 localhost.localdomain nginx[112202]: nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
May 31 11:12:29 localhost.localdomain nginx[112202]: nginx: configuration file /etc/nginx/nginx.conf test is successful
May 31 11:12:29 localhost.localdomain systemd[1]: Failed to read PID from file /run/nginx.pid: Invalid argument
May 31 11:12:29 localhost.localdomain systemd[1]: Started nginx - high performance web server.
有人过来并执行 ps 来查找并杀死 nginx：
[root@localhost tmp]# ps -ef | grep nginx
root 112205 1 0 11:12 ? 00:00:00 nginx: master process /usr/sbin/nginx -c /etc/nginx/nginx.conf
nginx 112207 112205 0 11:12 ? 00:00:00 nginx: worker process
root 112212 111775 0 11:12 pts/4 00:00:00 grep --color=auto nginx
[root@localhost tmp]# kill -9 112205
该日志现包含：
[root@localhost tmp]# journalctl --unit nginx
-- Logs begin at Sun 2015-04-05 10:36:30 BST, end at Sun 2015-05-31 11:12:57 BST. --
May 31 10:20:41 localhost.localdomain systemd[1]: Starting nginx - high performance web server...
May 31 10:20:41 localhost.localdomain nginx[111169]: nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
May 31 10:20:41 localhost.localdomain nginx[111169]: nginx: configuration file /etc/nginx/nginx.conf test is successful
May 31 10:20:41 localhost.localdomain systemd[1]: Failed to read PID from file /run/nginx.pid: Invalid argument
May 31 10:20:41 localhost.localdomain systemd[1]: Started nginx - high performance web server.
May 31 10:27:05 localhost.localdomain systemd[1]: Stopping nginx - high performance web server...
May 31 10:27:05 localhost.localdomain systemd[1]: Stopped nginx - high performance web server.
May 31 10:58:36 localhost.localdomain systemd[1]: Stopped nginx - high performance web server.
May 31 11:12:29 localhost.localdomain systemd[1]: Starting nginx - high performance web server...
May 31 11:12:29 localhost.localdomain nginx[112202]: nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
May 31 11:12:29 localhost.localdomain nginx[112202]: nginx: configuration file /etc/nginx/nginx.conf test is successful
May 31 11:12:29 localhost.localdomain systemd[1]: Failed to read PID from file /run/nginx.pid: Invalid argument
May 31 11:12:29 localhost.localdomain systemd[1]: Started nginx - high performance web server.
May 31 11:12:57 localhost.localdomain systemd[1]: nginx.service: main process exited, code=killed, status=9/KILL
May 31 11:12:57 localhost.localdomain kill[112215]: Usage:
May 31 11:12:57 localhost.localdomain kill[112215]: kill [options] <pid|name> [...]
May 31 11:12:57 localhost.localdomain kill[112215]: Options:
May 31 11:12:57 localhost.localdomain kill[112215]: -a, --all do not restrict the name-to-pid conversion to processes
May 31 11:12:57 localhost.localdomain kill[112215]: with the same uid as the present process
May 31 11:12:57 localhost.localdomain kill[112215]: -s, --signal <sig> send specified signal
May 31 11:12:57 localhost.localdomain kill[112215]: -q, --queue <sig> use sigqueue(2) rather than kill(2)
May 31 11:12:57 localhost.localdomain kill[112215]: -p, --pid print pids without signaling them
May 31 11:12:57 localhost.localdomain kill[112215]: -l, --list [=<signal>] list signal names, or convert one to a name
May 31 11:12:57 localhost.localdomain kill[112215]: -L, --table list signal names and numbers
May 31 11:12:57 localhost.localdomain kill[112215]: -h, --help display this help and exit
May 31 11:12:57 localhost.localdomain kill[112215]: -V, --version output version information and exit
May 31 11:12:57 localhost.localdomain kill[112215]: For more details see kill(1).
May 31 11:12:57 localhost.localdomain systemd[1]: nginx.service: control process exited, code=exited status=1
May 31 11:12:57 localhost.localdomain systemd[1]: Unit nginx.service entered failed state.
观察你只看到的那一列php包含作用于 nginx systemd 单元的进程的名称，systemd、nginx、kill 都列在那里。这有助于解释吗？
单元名称由文件名指定。在 Centos 7 上，我执行了：
(cfs)[root@localhost system]# pwd
/usr/lib/systemd/system
^?(cfs)[root@localhost system]# cp nginx.service newnginx.service
停止原有的nxginx：
(cfs)[root@localhost system]# service nginx stop
Redirecting to /bin/systemctl stop nginx.service
(cfs)[root@localhost system]# service h^Cinx stop
查看并启动“newnginx”：
(cfs)[root@localhost system]# service newnginx status
Redirecting to /bin/systemctl status newnginx.service
newnginx.service - nginx - high performance web server
Loaded: loaded (/usr/lib/systemd/system/newnginx.service; disabled)
Active: inactive (dead)
Docs: http://nginx.org/en/docs/
(cfs)[root@localhost system]# service newnginx start
Redirecting to /bin/systemctl start newnginx.service
Journalctl 现在列出了该newnginx单位：
(cfs)[root@localhost system]# journalctl --unit newnginx
-- Logs begin at Sun 2015-04-05 10:36:30 BST, end at Sun 2015-05-31 10:27:38 BST. --
May 31 10:27:38 localhost.localdomain systemd[1]: Starting nginx - high performance web server...
May 31 10:27:38 localhost.localdomain nginx[111311]: nginx: the configuration file /etc/nginx/nginx.conf syntax is o
May 31 10:27:38 localhost.localdomain nginx[111311]: nginx: configuration file /etc/nginx/nginx.conf test is success
May 31 10:27:38 localhost.localdomain systemd[1]: Failed to read PID from file /run/nginx.pid: Invalid argument
May 31 10:27:38 localhost.localdomain systemd[1]: Started nginx - high performance web server.
现在有两个 nginx systemd 单元：
# systemctl list-unit-files --all | grep nginx
newnginx.service disabled
nginx.service disabled
答案2
SyslogIdentifier=设置进程名称（“syslog 标签”），以作为发送到日志系统或内核日志缓冲区的日志行的前缀。如果未设置，则默认为执行进程的进程名称。此选项仅在 StandardOutput= 或 StandardError= 设置为 journal、syslog 或 kmsg（或与 +console 结合使用相同的设置）时才有用，并且仅适用于写入 stdout 或 stderr 的日志消息。
https://www.freedesktop.org/software/systemd/man/systemd.exec.html#SyslogIdentifier=
这将覆盖输出SYSLOG_IDENTIFIER中的字段journalctl。
# grep prvzn /etc/systemd/system/prvzn.service
ExecStart=/opt/infra/prvzn exec --config-dir ${CONFIG_DIR}
SyslogIdentifier=prvzn-foobar
journalctl 中的结果是这样的：
# journalctl | grep prvzn | tail -n1
Apr 30 08:29:16 ro01 prvzn-foobar[31787]: prvzn (info)2018/04/30 08:29:16 evaluation successful.
我同时运行着不同版本的 Ubuntu（14.04、16.04、17.10）和 CentOS（7）……我自己遇到的问题是 systemd 一直在快速变化，许多配置选项无法一致地工作，在某些情况下甚至在不同版本之间不可用。请查看特定版本的 systemd 的手册页。ymmv