Some more lines from /var/log/syslog of that same time. Looks like some process is running various scripts in /usr/lib/linux-boot-probes/ and /usr/lib/os-probes.
Jul 21 07:38:41 host systemd[1]: xen.service: Succeeded. Jul 21 07:38:41 host systemd[1]: Stopped LSB: Xen daemons. Jul 21 07:38:53 host kernel: SGI XFS with ACLs, security attributes, realtime, no debug enabled Jul 21 07:38:53 host kernel: JFS: nTxBlock = 7137, nTxLock = 57100 Jul 21 07:38:53 host kernel: QNX4 filesystem 0.2.3 registered. Jul 21 07:38:54 host kernel: raid6: sse2x1 gen() 4028 MB/s Jul 21 07:38:54 host kernel: raid6: sse2x1 xor() 3036 MB/s Jul 21 07:38:54 host kernel: raid6: sse2x2 gen() 4666 MB/s Jul 21 07:38:54 host kernel: raid6: sse2x2 xor() 3596 MB/s Jul 21 07:38:54 host kernel: raid6: sse2x4 gen() 5263 MB/s Jul 21 07:38:54 host kernel: raid6: sse2x4 xor() 3941 MB/s Jul 21 07:38:54 host kernel: raid6: using algorithm sse2x4 gen() 5263 MB/s Jul 21 07:38:54 host kernel: raid6: .... xor() 3941 MB/s, rmw enabled Jul 21 07:38:54 host kernel: raid6: using ssse3x2 recovery algorithm Jul 21 07:38:54 host kernel: xor: measuring software checksum speed Jul 21 07:38:54 host kernel: prefetch64-sse: 6630.000 MB/sec Jul 21 07:38:54 host kernel: generic_sse: 5853.000 MB/sec Jul 21 07:38:54 host kernel: xor: using function: prefetch64-sse (6630.000 MB/sec) Jul 21 07:38:54 host kernel: Btrfs loaded, crc32c=crc32c-intel Jul 21 07:38:54 host kernel: fuse init (API version 7.27) Jul 21 07:38:54 host systemd[1]: Mounting FUSE Control File System... Jul 21 07:38:54 host systemd[1]: Mounted FUSE Control File System. Jul 21 07:38:55 host os-prober[11566]: debug: running /usr/lib/os-probes/mounted/05efi on mounted /dev/sda1 (...) Jul 21 07:39:38 host 50mounted-tests[16816]: debug: /usr/lib/linux-boot-probes/mounted/40grub2 succeeded Jul 21 07:39:38 host systemd[1828]: var-lib-os\x2dprober-mount.mount: Succeeded. Jul 21 07:39:38 host systemd[1]: var-lib-os\x2dprober-mount.mount: Succeeded. Jul 21 07:39:38 host linux-boot-prober[16820]: debug: linux detected by /usr/lib/linux-boot-probes/50mounted-tests niek
