Linux中的系统日志在哪里？

Linux系统中的日志通常存储在/var/log目录中，该目录包含多种关键日志文件，如syslog或messages（记录系统日志）、auth.log（记录认证事件）、kern.log（记录内核消息）、dpkg.log或yum.log（记录软件包操作）、boot.log（记录启动信息）；可通过cat、tail -f或journalctl等命令查看日志内容；应用日志也常位于/var/log下的子目录，如Apache的apache2或httpd目录、MySQL的日志文件等；同时需注意日志权限通常需要sudo访问，且日志会通过logrotate进行轮换，旧日志可能以.gz压缩形式存在于类似syslog.1、syslog.2.gz等文件中。

System logs in Linux are typically stored in the /var/log directory. This is where most system-generated log files live, and it's the first place you should check if you're trying to troubleshoot an issue or monitor system behavior.

Common Log Files in /var/log

Here are some of the most important log files you’ll find in this directory:

• /var/log/syslog or /var/log/messages
  These contain general system logs. The exact name can vary by distribution — Debian-based systems usually use syslog, while Red Hat-based ones go with messages.

• /var/log/auth.log
  This file records all authentication-related events like login attempts (successful or failed), sudo usage, and SSH access.

• /var/log/kern.log
  Kernel-specific messages are logged here, which is helpful when debugging hardware or driver issues.

• /var/log/dpkg.log (Debian/Ubuntu) or /var/log/yum.log (RHEL/CentOS)
  These track package installations, updates, and removals.

• /var/log/boot.log
  Logs related to the system boot process. Not always enabled by default on all systems.

If you're tracking down a specific event, scanning through these files can give you clues about what went wrong and when.

How to View Log Files

You don’t need any special tools to read most log files — just basic command-line utilities will do:

• Use cat /var/log/syslog to view the full file
• Try tail -f /var/log/syslog to watch logs update in real time
• Run journalctl -u ssh (on systemd systems) to see logs for a specific service

Some distributions have moved to using journald, part of the systemd suite, which stores logs in binary format. You can access those with the journalctl command. For example:

• journalctl – view all logs
• journalctl -b – view logs from the current boot only
• journalctl --since "1 hour ago" – filter recent logs

Where Are Application Logs?

Not all logs come from the system itself. Many applications create their own log files under /var/log. For example:

• Apache web server logs are often in /var/log/apache2/ or /var/log/httpd/
• MySQL/MariaDB logs might be at /var/log/mysql.log or /var/log/mariadb.log
• Cron jobs usually leave traces in /var/log/cron.log

Check the configuration files of the application (often in /etc/) to find out exactly where they’re logging.

Also, some services allow you to customize log locations via config files, so don’t assume they always follow standard paths.

Permissions and Log Rotation

Keep in mind that most log files are owned by root, so you'll need elevated privileges (sudo) to read them.

Logs also get rotated regularly to prevent them from growing too large. This is handled by logrotate, usually configured in /etc/logrotate.conf and /etc/logrotate.d/.

Log rotation means older logs may not be in the main file anymore — look for files like /var/log/syslog.1, /var/log/syslog.2.gz, etc., depending on how many rotations have occurred.

That’s how you find and work with system logs in Linux — mostly centered around /var/log, with a few variations depending on your distro and setup.

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