rpmemd version 1.4

The PMDK repository on GitHub is the ultimate source of information on PMDK from release 2.0! For all questions and to submit eventual issues please follow to that repository. The PMDK documentation collected here should be valid up to the 1.13.1 release but is maintained only on a best-effort basis and may not reflect the latest state of the art.



rpmemd - librpmem target node process (EXPERIMENTAL)


$ rpmemd [--help] [--version] [<args>]


The rpmemd process is executed on target node by librpmem(7) library over ssh(1) and facilitates access to persistent memory over RDMA. The rpmemd should not be run manually under normal conditions.


Command line options overwrite the default rpmemd configuration, the global configuration file and the user configuration file.

-V, --version

Displays rpmemd version and exits.

-h, --help

Prints synopsis and list of parameters and exits.

-c, --config <path>

Custom configuration file location. If the custom configuration file is provided others are omitted. See CONFIGURATION FILES section for details.

All options described in CONFIGURATION FILES section are common for both the configuration file and the command line - the equivalent of the following line in the config file:

option = value


--option value

in the command line.

The following command line options: –persist-apm, –persist-general and –use-syslog should not be followed by any value. Presence of each of them in the command line turns on an appropriate option. See CONFIGURATION FILES section for details.

-r, --remove <poolset>

Remove a pool described by given pool set file descriptor. It is interpreted as a path to the pool set file relative to the pool set directory.

-f, --force

Ignore errors when removing a pool file using –remove option.


The rpmemd searches for the configuration files with following priorities:

  • The global configuration file located in /etc/rpmemd/rpmemd.conf.
  • The user configuration file located in the user home directory ($HOME/.rpmemd.conf).

The rpmemd can also read configuration from the custom configuration file provided using –config command line option. See OPTIONS section for details.

The default configuration is described in the DEFAULT CONFIGURATION section.

The configuration file is a plain text file. Each line of the configuration file can store only one configuration option defined as a key=value pair. Empty lines and lines starting with # are omitted.

The allowed options are:

  • log-file = <path> - log file location

  • poolset-dir = <path> - pool set files directory

  • persist-apm = {yes|no} - enable The Appliance Persistency Method. This option must be set only if the target platform has non-allocating writes IO enabled. See PERSISTENCY METHODS section for details.

  • persist-general = {yes|no} - enable The General Purpose Server Persistency Method. See PERSISTENCY METHODS section for details.

  • use-syslog = {yes|no} - use syslog(3) for logging messages instead of log file

  • log-level = <level> - set log level value. Accepted <level> values are:

    • err - error conditions
    • warn - warning conditions
    • notice - normal, but significant conditions
    • info - informational message
    • debug - debug-level message

The $HOME sub-string in the poolset-dir path is replaced with the current user home directory.


Example of the configuration file:

# This is an example of configuration file
log-file = $HOME/.logs/rpmemd.log
poolset-dir = $HOME/poolsets/
persist-apm = yes
persist-general = no
use-syslog = no # Use log file instead of syslog
log-level = info


The rpmemd default configuration is equivalent of the following configuration file:

log-file = /var/log/rpmemd.log
poolset-dir = $HOME
persist-apm = no
persist-general = yes
use-syslog = yes
log-level = err


The librpmem(7) supports two methods for making data written to remote persistent memory durable. The difference between the use of the two mechanisms is based on whether librpmem(7) will make use of non-allocating writes on the remote node.

  • The General Purpose Server Persistency Method does not have any requirements for the platform on which the target daemon runs and can be enabled by administrator using the persist-general option. This method utilize libpmem(7) persistency mechanisms on remote node and requires additional communication between initiator and remote node using the in-band connection.

  • The Appliance Persistency Method requires non-allocating writes enabled on the platform and can be enabled by administrator using persist-apm option. This method requires to issue an RDMA READ operation after the RDMA WRITE operations performed on requested chunk of memory.

“Non-allocating write requests” is the Intel Integrated IO Controller mode where all incoming PCIe writes will utilize non-allocating buffers for the write requests. Non-allocating writes are guaranteed to bypass all of the CPU caches and force the write requests to flow directly to the Integrated Memory Controller without delay.

The rpmemd dynamically choose the appropriate persistency method and the flushing to persistence primitive for GPSPM for each opened pool set name depending on available persistency methods and whether all pool set parts are stored in the persistent memory.

If the Appliance Persistency Method is enabled and the pool set is stored in the persistent memory rpmemd will use the Appliance Persistency Method. If the pool set is NOT stored in the persistent memory it will fallback to the General Puropose Server Persistency Method with pmem_msync(3).

If the General Puropose Server Persistency Method is enabled and the pool set is stored in the persistent memory rpmemd will use pmem_persist(3). If the pool set is NOT stored in the persistent momory it will use pmem_msync(3).

See pmem_persist(3) and pmem_msync(3) for more details.


ssh(1), pmem_msync(3), pmem_persist(3), syslog(3), libpmem(7), libpmemobj(7), librpmem(7) and https://pmem.io

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