Why in dmesg centos 6 I see all messages from the moment of loading, but in dmesg gentoo only from a certain moment?

Question

linux

There is an old el6 server (server A):

# uname -a
Linux aaa.bbb.ccc 2.6.32-754.9.1.el6.centos.plus.x86_64 #1 SMP Thu Dec 6 08:03:42 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

There is a server on Calculate Linux (server B):

# uname -a
Linux ddd.bbb.ccc 4.19.29-calculate #2 SMP PREEMPT Wed Mar 20 18:49:43 +07 2019 x86_64 Intel(R) Xeon(R) CPU E5-2620 v4 @ 2.10GHz GenuineIntel GNU/Linux

Why do I see messages in server A's dmesg right from the very beginning of the download:

Initializing cgroup subsys cpuset
Initializing cgroup subsys cpu
Linux version 2.6.32-754.9.1.el6.centos.plus.x86_64 ([email protected]) (gcc version 4.4.7 201203
13 (Red Hat 4.4.7-23) (GCC) ) #1 SMP Thu Dec 6 08:03:42 UTC 2018
Command line: ro root=/dev/mapper/vg_xxx-lv_root rd_NO_LUKS LANG=en_US.UTF-8 rd_NO_MD SYSFONT=latarcyrhe
b-sun16 crashkernel=auto rd_LVM_LV=vg_xxx/lv_root rd_LVM_LV=vg_xxx/lv_swap  KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM rhgb nopti nospectre_v2 quiet
KERNEL supported cpus:
  Intel GenuineIntel
  AMD AuthenticAMD
  Centaur CentaurHauls
...

And in dmesg of server B - only from a certain moment, and everything that happened before this moment does not get into dmesg:

[    0.361397] pci 0000:00:18.0:   bridge window [mem 0xe7900000-0xe79fffff 64bit pref]
[    0.361440] pci 0000:00:18.1: PCI bridge to [bus 1c]
[    0.361451] pci 0000:00:18.1:   bridge window [io  0xb000-0xbfff]
[    0.361481] pci 0000:00:18.1:   bridge window [mem 0xfcd00000-0xfcdfffff]
[    0.361501] pci 0000:00:18.1:   bridge window [mem 0xe7500000-0xe75fffff 64bit pref]
...

and how to make it so that on server B it was like on server A (if at all possible)?

Answer 1

Perhaps a small kernel log buffer is set.
Pass log_buf_len=4096K to the kernel, for example.