Setting a CHPID logically online or offline

Red Hat Enterprise Linux 8.6 LPAR mode z/VM guest KVM guest

Directories that represent CHPIDs contain a status attribute that you can use to set the CHPID logically online or offline.

Before you begin

Do not set all CHPIDs that connect a vital device offline. For example, Linux® will crash if you set all CHPIDs for the root device offline.

About this task

When a CHPID has been set logically offline from a particular Linux instance, the CHPID is, in effect, offline for this Linux instance. A CHPID that is shared by multiple operating system instances can be logically online to some instances and offline to others. A CHPID can also be logically online to Linux while it has been varied off at the SE.

Procedure

To set a CHPID logically online, set its status attribute to online by writing the value on to it. To set a CHPID logically offline, set its status attribute to offline by writing off to it.

Issue a command of this form:

# echo <value> > /sys/devices/css0/chp0.<CHPID>/status

where:

<CHPID>: is a two digit hexadecimal CHPID.
<value>: is either on or off.

Examples

To set a CHPID 0x4a logically offline issue:

# echo off > /sys/devices/css0/chp0.4a/status

To read the status attribute to confirm that the CHPID is logically offline issue:
```
# cat /sys/devices/css0/chp0.4a/status
offline
```
To set the same CHPID logically online issue:
```
# echo on > /sys/devices/css0/chp0.4a/status
```
To read the status attribute to confirm that the CHPID is logically online issue:
```
# cat /sys/devices/css0/chp0.4a/status
online
```