Linux v5.16.1 - um
# SPDX-License-Identifier: GPL-2.0
menu "UML-specific options"
select HAVE_FUTEX_CMPXCHG if FUTEX
select NO_DMA if !UML_DMA_EMULATION
select TTY # Needed for line.c
bool "disable IOMEM" if EXPERT
depends on !INDIRECT_IOMEM
range 1 1
bool "Force a static link"
depends on CC_CAN_LINK_STATIC_NO_RUNTIME_DEPS || !MAY_HAVE_RUNTIME_DEPS
This option gives you the ability to force a static link of UML.
Normally, UML is linked as a shared binary. This is inconvenient for
use in a chroot jail. So, if you intend to run UML inside a chroot,
you probably want to say Y here.
Additionally, this option enables using higher memory spaces (up to
2.75G) for UML.
NOTE: This option is incompatible with some networking features which
depend on features that require being dynamically loaded (like NSS).
depends on STATIC_LINK
depends on !LD_SCRIPT_STATIC
select MODULE_REL_CRCS if MODVERSIONS
bool "set rpath in the binary" if EXPERT
depends on LD_SCRIPT_DYN
Add /lib (and /lib64 for 64-bit) to the linux binary's rpath
You may need to turn this off if compiling for nix systems
that have their libraries in random /nix directories and
might otherwise unexpected use libraries from /lib or /lib64
instead of the desired ones.
tristate "Host filesystem"
While the User-Mode Linux port uses its own root file system for
booting and normal file access, this module lets the UML user
access files stored on the host. It does not require any
network connection between the Host and UML. An example use of
this might be:
mount none /tmp/fromhost -t hostfs -o /tmp/umlshare
where /tmp/fromhost is an empty directory inside UML and
/tmp/umlshare is a directory on the host with files the UML user
wishes to access.
For more information, see
If you'd like to be able to work with files stored on the host,
say Y or M here; otherwise say N.
bool "Management console"
depends on PROC_FS
The user mode linux management console is a low-level interface to
the kernel, somewhat like the i386 SysRq interface. Since there is
a full-blown operating system running under every user mode linux
instance, there is much greater flexibility possible than with the
If you answer 'Y' to this option, to use this feature, you need the
mconsole client (called uml_mconsole) which is present in CVS in
2.4.5-9um and later (path /tools/mconsole), and is also in the
distribution RPM package in 2.4.6 and later.
It is safe to say 'Y' here.
bool "Magic SysRq key"
depends on MCONSOLE
If you say Y here, you will have some control over the system even
if the system crashes for example during kernel debugging (e.g., you
will be able to flush the buffer cache to disk, reboot the system
immediately or dump some status information). A key for each of the
possible requests is provided.
This is the feature normally accomplished by pressing a key
while holding SysRq (Alt+PrintScreen).
On UML, this is accomplished by sending a "sysrq" command with
mconsole, followed by the letter for the requested command.
The keys are documented in <file:Documentation/admin-guide/sysrq.rst>. Don't say Y
unless you really know what this hack does.
int "Kernel stack size order"
default 2 if 64BIT
range 2 10 if 64BIT
default 1 if !64BIT
This option determines the size of UML kernel stacks. They will
be 1 << order pages. The default is OK unless you're running Valgrind
on UML, in which case, set this to 3.
It is possible to reduce the stack to 1 for 64BIT and 0 for 32BIT on
older (pre-2017) CPUs. It is not recommended on newer CPUs due to the
increase in the size of the state which needs to be saved when handling
tristate "iomem emulation driver"
This driver allows a host file to be used as emulated IO memory inside
default 3 if 3_LEVEL_PGTABLES
prompt "Support time-travel mode (e.g. for test execution)"
# inf-cpu mode is incompatible with the benchmarking
depends on !RAID6_PQ_BENCHMARK
depends on !SMP
Enable this option to support time travel inside the UML instance.
After enabling this option, two modes are accessible at runtime
(selected by the kernel command line), see the kernel's command-
line help for more details.
It is safe to say Y, but you probably don't need this.