Linux

RedHat Enterprise Server

Handy Scripts and Commands

List WWPNs

    for host in /sys/class/fc_host/host*; do
        echo "WWPN and state for $host:"
        cat "$host/port_name" | sed 's/^0x//'
        cat "$host/port_state"
        echo
    done

Procedures

Updating RHEL Minor Version

Set the release version
```
subscription-manager release --set=8.7
```
Update
```
dnf update
```
Reboot to activate new kernel
```
reboot
```
Verify
```
uname -r
cat /etc/redhat-release
```

Changing The Default Kernel

Simple way common to RHEL8 and RHEL9

Confirmation before the change

grubby --default-kernel
# /boot/vmlinuz-5.14.0-70.30.1.el9_0.x86_64

uname -r
# 5.14.0-70.30.1.el9_0.x86_64

Show installed kernel list ( You can count 0,1,.. from the top of the title line)

grubby --info=ALL | grep title
# title="Red Hat Enterprise Linux (5.14.0-70.30.1.el9_0.x86_64) 9.0 (Plow)"    <---0
# title="Red Hat Enterprise Linux (5.14.0-70.13.1.el9_0.x86_64) 9.0 (Plow)"    <---1

Set the default kernel
```
grub2-set-default 1
```

Confirmation after the change

grubby --default-kernel
# /boot/vmlinuz-5.14.0-70.13.1.el9_0.x86_64

reboot the system
```
reboot
```

Confirmation after system reboot

uname -r 
# 5.14.0-70.13.1.el9_0.x86_64

grubby --default-kernel
# /boot/vmlinuz-5.14.0-70.13.1.el9_0.x86_64

Downgrade kernel-devel to match system kernel

    uname -r