How to check last boot time in Linux

Checking the last boot time confirms when the current system session began, which helps line up reboots with kernel changes, maintenance windows, outages, or service behavior that started after a restart.

Linux exposes the current boot in a few different places. uptime -s prints the boot timestamp reported by the running system, who -b prints the last boot event from the current login-accounting record, and last reboot reads retained reboot history from /var/log/wtmp.

These commands are common on current full Linux installations, but shared-kernel containers usually report the host boot rather than the container start. Minimal systems may also lack the retained boot records that who -b and last reboot use, and some non-procps uptime builds do not support -s.

Steps to check last boot time in Linux:

Print the current boot timestamp directly from the running system.
```
$ uptime -s
2026-04-14 19:30:16
```
This is the quickest direct answer for the current boot and it includes seconds, which makes it useful for incident timelines and reboot verification.
Cross-check the last recorded boot event from login accounting.
```
$ who -b
         system boot  2026-04-14 19:30
```
who -b usually reports only to the minute. If it prints nothing, the current system is not exposing the boot record through the usual login-accounting files.
Show the current reboot record in ISO 8601 format when a timezone-aware timestamp or retained reboot history matters.
```
$ last reboot -1 --time-format iso
reboot   system boot  6.14.0-37-generi 2026-04-14T19:30:21+08:00   still running

wtmp begins 2024-04-27T12:34:07+08:00
```
The first line is the active boot record. The trailing wtmp begins … line shows how far back the retained reboot history currently goes, and on systems without a stored reboot entry it may be the only line printed.