What means the content in the square brackets in the following Debian 13 logs?
``` [48458.407305] spd5118 0-0050: Failed to write b = 0: -6 ```
Aug 4, 9:14pm
In Debian (and Linux in general) logs, the content inside square brackets at the beginning of a log line, such as [48458.407305], represents the kernel timestamp. Here's what it means:
Kernel Timestamp
Format:[<seconds>.<microseconds>]
Meaning:
48458: The number of seconds since the system booted.
407305: The number of microseconds (or fractions of a second) since the last full second.
This timestamp is generated by the Linux kernel and indicates when the event occurred relative to the system's uptime. It is not a wall-clock time (like "2026-08-04 14:30:00"), but rather a monotonically increasing counter starting from 0.000000 when the kernel initializes.
Why is this useful?
Debugging: Helps correlate events in the kernel log with system uptime.
Ordering: Allows you to see the exact sequence of kernel events, even if they happen very quickly.
Performance: Useful for measuring how long certain operations take in the kernel.
Aug 4, 9:14pm
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