journalctl命令来自英文词组journal control的缩写，其功能是查看指定的日志信息。在RHEL 7/CentOS 7及以后版本的Linux系统中，systemd服务统一管理了所有服务的启动日志，带来的好处就是可以只用journalctl一个命令来查看全部的日志信息了。
语法格式：journalctl 参数 对象
常用参数：
| -a | 显示所有字段信息 | -o | 设置日志条目格式 | |
| -b | 显示本次系统启动的日志信息 | -p | 依据优先级筛选 | |
| -c | 从指定位置开始显示条目 | -q | 静默执行模式 | |
| -D | 设置目录路径 | -r | 反选内容后再显示 | |
| -f | 追踪日志内容 | -u | 显示指定服务的日志 | |
| -k | 显示内核日志 | --help | 显示帮助信息 | |
| -m | 显示所有可用日志 | --version | 显示版本信息 | |
| -n | 设置日志条数 |
参考示例
查看系统中全部的日志信息：
[root@linuxcool ~]# journalctl -- Logs begin at Thu 2023-05-18 02:12:18 CST, end at Sat 2023-05-28 13:15:02 CS> May 18 02:12:18 linuxprobe.com kernel: Linux version 4.18.0-80.el8.x86_64 (mock> May 18 02:12:18 linuxprobe.com kernel: Command line: BOOT_IMAGE=(hd0,msdos1)/vm> May 18 02:12:18 linuxprobe.com kernel: Disabled fast string operations ………………省略部分输出信息………………
指定查看内核日志信息：
[root@linuxcool ~]# journalctl -k -- Logs begin at Thu 2023-05-18 02:12:18 CST, end at Sat 2023-05-28 13:15:02 CS> May 18 02:12:18 linuxprobe.com kernel: Linux version 4.18.0-80.el8.x86_64 (mock> May 18 02:12:18 linuxprobe.com kernel: Command line: BOOT_IMAGE=(hd0,msdos1)/vm> May 18 02:12:18 linuxprobe.com kernel: Disabled fast string operations ………………省略部分输出信息………………
指定查看本次系统启动的日志信息：
[root@linuxcool ~]# journalctl -b -- Logs begin at Thu 2023-05-18 02:12:18 CST, end at Sat 2023-05-28 13:15:02 CS> May 18 02:12:18 linuxprobe.com kernel: x86/fpu: Supporting XSAVE feature 0x001:> May 18 02:12:18 linuxprobe.com kernel: x86/fpu: Supporting XSAVE feature 0x002:> May 18 02:12:18 linuxprobe.com kernel: x86/fpu: Supporting XSAVE feature 0x004:> ………………省略部分输出信息………………
指定查看某个服务程序的日志信息：
[root@linuxcool ~]# journalctl -u sshd -- Logs begin at Thu 2023-05-18 02:12:18 CST, end at Sat 2023-05-28 13:17:01 CS> May 18 02:12:22 linuxcool.com systemd[1]: Starting OpenSSH server daemon... May 18 02:12:22 linuxcool.com sshd[1109]: Server listening on 0.0.0.0 port 22. May 18 02:12:22 linuxcool.com sshd[1109]: Server listening on :: port 22. May 18 02:12:22 linuxcool.com systemd[1]: Started OpenSSH server daemon ………………省略部分输出信息………………
指定查看最近10条日志信息：
[root@linuxcool ~]# journalctl -n 10 -- Logs begin at Thu 2023-05-18 02:12:18 CST, end at Sat 2023-05-28 13:17:01 CS> May 28 13:01:01 linuxcool.com run-parts[3541]: (/etc/cron.hourly) finished 0ana> May 28 13:15:00 linuxcool.com dbus-daemon[980]: [system] Activating via systemd> May 28 13:15:00 linuxcool.com systemd[1]: Starting Fingerprint Authentication D> May 28 13:15:00 linuxcool.com dbus-daemon[980]: [system] Successfully activated> May 28 13:15:00 linuxcool.com systemd[1]: Started Fingerprint Authentication Da> May 28 13:15:02 linuxcool.com gdm-password][3666]: gkr-pam: unlocked login keyr> May 28 13:15:02 linuxcool.com NetworkManager[1093]: [1653714902.2810] a> May 28 13:17:01 linuxcool.com anacron[2921]: Job `cron.monthly' started May 28 13:17:01 linuxcool.com anacron[2921]: Job `cron.monthly' terminated May 28 13:17:01 linuxcool.com anacron[2921]: Normal exit (3 jobs run)
持续追踪最新的日志信息，保持刷新内容：
[root@linuxcool ~]# journalctl -f -- Logs begin at Thu 2023-05-18 02:12:18 CST. -- May 28 13:01:01 linuxcool.com run-parts[3541]: (/etc/cron.hourly) finished 0anacron May 28 13:15:00 linuxcool.com dbus-daemon[980]: [system] Activating via systemd: service name='net.reactivated.Fprint' unit='fprintd.service' requested by ':1.177' (uid=0 pid=2222 comm="/usr/bin/gnome-shell " label="unconfined_u: unconfined_r:unconfined_t:s0-s0:c0.c1023") May 28 13:15:00 linuxcool.com systemd[1]: Starting Fingerprint Authentication Daemon... May 28 13:15:00 linuxcool.com dbus-daemon[980]: [system] Successfully activated service 'net.reactivated.Fprint' May 28 13:15:00 linuxcool.com systemd[1]: Started Fingerprint Authentication Daemon. May 28 13:15:02 linuxcool.com gdm-password][3666]: gkr-pam: unlocked login keyring May 28 13:15:02 linuxcool.com NetworkManager[1093]: [1653714902.2810] agent-manager: req[0x7fdcc8007190, :1.177/org.gnome.Shell.NetworkAgent/0]: agent registered May 28 13:17:01 linuxcool.com anacron[2921]: Job `cron.monthly' started May 28 13:17:01 linuxcool.com anacron[2921]: Job `cron.monthly' terminated May 28 13:17:01 linuxcool.com anacron[2921]: Normal exit (3 jobs run) ………………省略部分输出信息………………
