CHMEM(8)		     System Administration		      CHMEM(8)

NAME
       chmem - configure memory

SYNOPSIS
       chmem [-h] [-V*] [-v] [-e|-d] [SIZE|RANGE -b BLOCKRANGE] [-z ZONE]

DESCRIPTION
       The chmem command sets a particular size or range of memory online or
       offline.

       •   Specify SIZE as <size>[m|M|g|G]. With m or M, <size> specifies the
	   memory size in MiB (1024 x 1024 bytes). With g or G, <size>
	   specifies the memory size in GiB (1024 x 1024 x 1024 bytes). The
	   default unit is MiB.

       •   Specify RANGE in the form 0x<start>-0x<end> as shown in the output
	   of the lsmem(1) command. <start> is the hexadecimal address of the
	   first byte and <end> is the hexadecimal address of the last byte in
	   the memory range.

       •   Specify BLOCKRANGE in the form <first>-<last> or <block> as shown
	   in the output of the lsmem(1) command. <first> is the number of the
	   first memory block and <last> is the number of the last memory
	   block in the memory range. Alternatively a single block can be
	   specified. BLOCKRANGE requires the --blocks option.

       •   Specify ZONE as the name of a memory zone, as shown in the output
	   of the lsmem -o +ZONES command. The output shows one or more valid
	   memory zones for each memory range. If multiple zones are shown,
	   then the memory range currently belongs to the first zone. By
	   default, chmem will set memory online to the zone Movable, if this
	   is among the valid zones. This default can be changed by specifying
	   the --zone option with another valid zone. For memory ballooning,
	   it is recommended to select the zone Movable for memory online and
	   offline, if possible. Memory in this zone is much more likely to be
	   able to be offlined again, but it cannot be used for arbitrary
	   kernel allocations, only for migratable pages (e.g., anonymous and
	   page cache pages). Use the --help option to see all available
	   zones.

       SIZE and RANGE must be aligned to the Linux memory block size, as shown
       in the output of the lsmem(1) command.

       Setting memory online can fail for various reasons. On virtualized
       systems it can fail if the hypervisor does not have enough memory left,
       for example because memory was overcommitted. Setting memory offline
       can fail if Linux cannot free the memory. If only part of the requested
       memory can be set online or offline, a message tells you how much
       memory was set online or offline instead of the requested amount.

       When setting memory online chmem starts with the lowest memory block
       numbers. When setting memory offline chmem starts with the highest
       memory block numbers.

OPTIONS
       -b, --blocks
	   Use a BLOCKRANGE parameter instead of RANGE or SIZE for the
	   --enable and --disable options.

       -d, --disable
	   Set the specified RANGE, SIZE, or BLOCKRANGE of memory offline.

       -e, --enable
	   Set the specified RANGE, SIZE, or BLOCKRANGE of memory online.

       -z, --zone
	   Select the memory ZONE where to set the specified RANGE, SIZE, or
	   BLOCKRANGE of memory online or offline. By default, memory will be
	   set online to the zone Movable, if possible.

       -v, --verbose
	   Verbose mode. Causes chmem to print debugging messages about its
	   progress.

       -h, --help
	   Display help text and exit.

       -V, --version
	   Display version and exit.

EXIT STATUS
       chmem has the following exit status values:

       0
	   success

       1
	   failure

       64
	   partial success

EXAMPLE
       chmem --enable 1024
	   This command requests 1024 MiB of memory to be set online.

       chmem -e 2g
	   This command requests 2 GiB of memory to be set online.

       chmem --disable 0x00000000e4000000-0x00000000f3ffffff
	   This command requests the memory range starting with
	   0x00000000e4000000 and ending with 0x00000000f3ffffff to be set
	   offline.

       chmem -b -d 10
	   This command requests the memory block number 10 to be set offline.

SEE ALSO
       lsmem(1)

REPORTING BUGS
       For bug reports, use the issue tracker
       <https://github.com/util-linux/util-linux/issues>.

AVAILABILITY
       The chmem command is part of the util-linux package which can be
       downloaded from Linux Kernel Archive
       <https://www.kernel.org/pub/linux/utils/util-linux/>.

util-linux 2.41.2		  2025-09-22			      CHMEM(8)