So you're stuck in the Anaconda installer and can't copy files to and from to troubleshoot an issue?  

Could not load host key /etc/ssh/ssh_host_rsa_key

or you're getting something like this after some FS XFS corruption due to storage failure:  

[  358.344254] XFS (dm-0): Metadata corruption detected at xfs_inode_buf_verify+0x79/0x100 [xfs], xfs_inode block 0x3c44aa0
[  358.349741] XFS (dm-0): Unmount and run xfs_repair
[  358.352350] XFS (dm-0): First 64 bytes of corrupted metadata buffer:
[  358.355398] ffff92237a9e2000: 35 64 64 39 38 38 37 36 35 34 36 65 39 30 65 66  5dd98876546e90ef
[  358.359107] ffff92237a9e2010: 66 65 36 32 64 38 34 30 37 37 62 65 36 66 33 37  fe62d84077be6f37
[  358.362794] ffff92237a9e2020: 62 62 37 65 62 63 31 66 61 37 31 38 65 35 36 64  bb7ebc1fa718e56d
[  358.366488] ffff92237a9e2030: 34 30 62 32 64 33 63 36 35 30 34 66 33 62 38 66  40b2d3c6504f3b8f
[  358.370229] XFS (dm-0): metadata I/O error: block 0x3c44aa0 ("xfs_trans_read_buf_map") error 117 numblks 16
[  358.375987] XFS (dm-0): I/O Error Detected. Shutting down filesystem
[  358.379058] XFS (dm-0): Please umount the filesystem and rectify the problem(s)

Run the following commands to enable networking and the SSHD daemon:  

1. ssh-keygen
2. cp /root/.ssh/id_rsa /etc/ssh/ssh_host_rsa_key
3. cp /etc/ssh/sshd_config.anaconda /etc/ssh/sshd_config
4. /sbin/sshd -p 22
5. ip addr add 10.0.0.100/24 dev ens3
6. (THIS) ip route add 10.0.0.0/24 via 10.0.0.1 dev ens3
7. (OR) ip route add default via 10.0.0.1 dev ens3
8. ip link set ens3 up

SSH in to troubleshoot:  

[root@remote01 ~]# ssh 10.0.0.100
Warning: Permanently added '10.0.0.100' (RSA) to the list of known hosts.
[anaconda root@localhost ~]#

Particularly handy when troubleshooting boot issues. Running tail -f /tmp/*.log will now be possible remotely while troubleshooting boot problems.  

Use the same procedure to access corrupted filesystems on environments.  

BONUS: Repair XFS Filesystem in Maintenance

Here's how to recover a corrupted XFS filesystem by logging into the system using the above steps.

vgscan -v –mknodes
vgchange -a y
ls -altri /dev/centos/*

Verify LV's exist.  Repair.  Example:

xfs_repair /dev/centos/home
xfs_repair /dev/centos/root

If you run into this:

ERROR: The filesystem has valuable metadata changes in a log which needs to
be replayed.  Mount the filesystem to replay the log, and unmount it before
re-running xfs_repair.  If you are unable to mount the filesystem, then use
the -L option to destroy the log and attempt a repair.
Note that destroying the log may cause corruption — please attempt a mount
of the filesystem before doing this.

Simply follow instructions and mount it:

[anaconda root@localhost ~]# mkdir lv-root
[anaconda root@localhost ~]# mount /dev/centos/root lv-root
[anaconda root@localhost ~]# cd lv-root/
[anaconda root@localhost lv-root]# ls
bin   dev  home  lib64       mds.xyz  misc  n    nix.mds.xyz  proc  run   srv               sys  usr
boot  etc  lib   lost+found  media    mnt   net  opt          root  sbin  sssd-updates.txt  tmp  var
[anaconda root@localhost lv-root]#

This replays the journal log.  After this, you should be able to boot into the system. 

BONUS: Install RPM in recovery.

Once you complete the above, mount the failed systems folders over a directory of your choice.  For example: 

mkdir lv-root; mount /dev/mapper/centos-root lv-root
mkdir lv-home mount /dev/mapper/centos-home lv-home

chroot lv-root

mknod -m 666 /dev/random c 1 8
mknod -m 666 /dev/urandom c 1 9

Install and update a package in an attempt to fix the environment.

[anaconda root@localhost /]# yum search kernel
================== N/S matched: kernel ===========================
<SOME PACKAGE>.x86_64 : The Linux kernel

Then install:

[anaconda root@localhost /]# yum update <SOME PACKAGE>.x86_64
Installed:
  <SOME PACKAGE.x86_64 0:3.10.0-1062.18.1.el7

Dependency Updated:
  <SOME PACKAGE DEPENDENCY>.noarch 0:20190429-72.gitddde598.el7

Complete!
[anaconda root@localhost /]#

BONUS: Install RPM in recovery. ( METHOD 2 )

1. Mount the ISO or DVD.  Ideally the Everything DVD of CentOS.
2. Select Troubleshooting -> Rescue a CentOS Linux System -> Continue.
3. Once on the command prompt, type cd /mnt/install/repo/Packages
4. mkdir /mnt/sysimage/root/kernel; cp -ip kernel* /mnt/sysimage/root/kernel
5. chroot /mnt/sysimage
6. cd /root/kernel
7. yum install kernel*
8. ( Optional )  Edit /etc/default/grub in case custom parameters are needed.
9. grub2-mkconfig -o /boot/grub2/grub.cfg
10. exit
11. sync;sync; reboot
12. Login and Enjoy!

The above steps are a great replacement for single user mode such as using single or init=/bin/bash.  The filesystems on the original OS remain unmounted allowing a full range of troubleshooting options. 

Hope this helps.

Thx,