Using the magic sysrequest feature

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Ubuntu 22.04 LTS LPAR mode z/VM guest KVM guest

Whether magic sysrequest functions are available and how to call them depends on your terminal.

  • To call the magic sysrequest functions on the VT220 terminal or on hvc0, enter the single character Ctrl+o followed by the character for the particular function.

    You can call the magic sysrequest functions from the hvc0 terminal device if it is present and is activated to receive Linux® kernel messages.

  • To call the magic sysrequest functions on a line-mode terminal, enter the 2 characters ^- (caret and hyphen) followed by a third character that specifies the particular function.

Table 1 provides an overview of the commands for the magic sysrequest functions:

Table 1. Magic sysrequest functions
On line-mode terminals, enter On hvc0 and the VT220 terminal, enter To
^-b Crtl+ob Re-IPL immediately.
^-c Crtl+oc Crash through a forced kernel panic.
^-s Crtl+os Emergency sync all file systems.
^-u Crtl+ou Emergency remount all mounted file systems read-only.
^-t Crtl+ot Show task info.
^-m Crtl+om Show memory.

^-
followed by a digit
(0 - 9)

Crtl+o

followed by a digit
(0 - 9)

Set the console log level.
^-e Crtl+oe Send the TERM signal to end all tasks except init.
^-i Crtl+oi Send the KILL signal to end all tasks except init.
^-p Crtl+op Obtain debug information about the CPU-measurement counter facility.
Note: In Table 1 Crtl+o means pressing o key while holding down the control key.

Table 1 lists the main magic sysrequest functions that are known to work on Ubuntu Server 22.04 LTS. For a more comprehensive list of functions, see /linux-doc/html/_sources/admin-guide/sysrq.rst.txt in the linux-doc package. Some of the listed functions might not work on your system.