Contents
What is Journalctl?
Journalctl is a utility for querying and displaying logs from journald, systemd’s logging service. Since journald stores log data in a binary format instead of a plaintext format, journalctl is the standard way of reading log messages processed by journald.
What is dmesg used for?
dmesg is used to examine or control the kernel ring buffer. The default action is to display all messages from the kernel ring buffer.
What’s in var log?
The main log file a) /var/log/messages – Contains global system messages, including the messages that are logged during system startup. There are several things that are logged in /var/log/messages including mail, cron, daemon, kern, auth, etc.
What’s the difference between dmesg output and / var / log / messages?
/var/log/messages includes all the system messages including from starting of the system along with the messages in dmesg. In a nutshell logs from dmesg are dumped in /var/log/messages. /var/log/messages maintain the general system activity logs and dmesg maintains only the kernel logs.
How is journalctl used to read log messages?
Since journald stores log data in a binary format instead of a plaintext format, journalctl is the standard way of reading log messages processed by journald. In the following paragraphs, we’ll show you several ways of using journalctl to retrieve, format, and analyze your logs.
When to use dmesg in the operating system?
This information is also sent in real time to syslogd or klogd, when they are running, and ends up in /var/log/messages; when dmesg is most useful is in capturing boot-time messages from before syslogd and/or klogd started, so that they will be properly logged. That depends on the operating system.
What’s the difference between var / log / messages and journald?
This is relevant because you won’t be finding /var/log/messages that often anymore. journald doesn’t write plaintext logs — it uses its own, compressed and partially authenticated format. Search online for e.g. journalctl cheatsheet, or just study man 8 systemd-journald, man 1 journalctl yourself.