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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | QUICK START GUIDE | NOTES | SEE ALSO | COLOPHON |
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ibacm(8) ibacm ibacm(8)
ibacm - address and route resolution services for InfiniBand.
ibacm [-D] [-P] [-A addr_file] [-O option_file]
The IB ACM implements and provides a framework for name, address,
and route (path) resolution services over InfiniBand. It is
intended to address connection setup scalability issues running
MPI applications on large clusters. The IB ACM provides
information needed to establish a connection, but does not
implement the CM protocol.
A primary user of the ibacm service is the librdmacm library.
This enables applications to make use of the ibacm service without
code changes or needing to be aware that the service is in use.
librdmacm versions 1.0.12 - 1.0.15 can invoke IB ACM services when
built using the --with-ib_acm option. Version 1.0.16 and newer of
librdmacm will automatically use the IB ACM if it is installed.
The IB ACM services tie in under the rdma_resolve_addr,
rdma_resolve_route, and rdma_getaddrinfo routines. For maximum
benefit, the rdma_getaddrinfo routine should be used, however
existing applications should still see significant connection
scaling benefits using the calls available in librdmacm 1.0.11 and
previous releases.
The IB ACM is focused on being scalable, efficient, and
extensible. It implements a plugin architecture that allows a
vendor to supply its proprietary provider in addition to the
default provider. The current default provider implementation
ibacmp limits network traffic, SA interactions, and centralized
services. Ibacmp supports multiple resolution protocols in order
to handle different fabric topologies.
The IB ACM package is comprised of three components: the ibacm
core service, the default provider ibacmp shared library, and a
test/configuration utility - ib_acme. All three are userspace
components and are available for Linux. Additional details are
given below.
-D run in daemon mode (default)
-P run as standard process
-A addr_file
address configuration file
-O option_file
option configuration file
--systemd
Enable systemd integration. This includes optional socket
activation of the daemon's listening socket.
1. Prerequisites: libibverbs and libibumad must be installed. The
IB stack should be running with IPoIB configured. These steps
assume that the user has administrative privileges.
2. Install the IB ACM package. This installs ibacm, ibacmp,
ib_acme, and init.d scripts.
3. Run 'ibacm' as administrator to start the ibacm daemon.
4. Optionally, run 'ib_acme -d <dest_ip> -v' to verify that the
ibacm service is running.
5. Install librdmacm, using the build option --with-ib_acm if
needed. This build option is not needed with librdmacm 1.0.17 or
newer. The librdmacm will automatically use the ibacm service.
On failures, the librdmacm will fall back to normal resolution.
6. You can use ib_acme -P to gather performance statistics from
the local ibacm daemon to see if the service is working correctly.
Similarly, the command ib_acme -e could be used to enumerate all
endpoints created by the local ibacm service.
ib_acme:
The ib_acme program serves a dual role. It acts as a utility to
test ibacm operation and help verify if the ibacm service and
selected protocol is usable for a given cluster configuration.
Additionally, it automatically generates ibacm configuration files
to assist with or eliminate manual setup.
ibacm configuration files:
The ibacm service relies on two configuration files.
The ibacm_addr.cfg file contains name and address mappings for
each IB <device, port, pkey> endpoint. Although the names in the
ibacm_addr.cfg file can be anything, ib_acme maps the host name to
the IB endpoints. IP addresses, on the other hand, are assigned
dynamically. If the address file cannot be found, the ibacm
service will attempt to create one using default values.
The ibacm_opts.cfg file provides a set of configurable options for
the ibacm core service and default provider, such as timeout,
number of retries, logging level, etc. ib_acme generates the
ibacm_opts.cfg file using static information. If an option file
cannot be found, ibacm will use default values.
ibacm:
The ibacm service is responsible for resolving names and addresses
to InfiniBand path information and caching such data. It should
execute with administrative privileges.
The ibacm implements a client interface over TCP sockets, which is
abstracted by the librdmacm library. One or more providers can be
loaded by the core service, depending on the configuration. In
the default provider ibacmp, one or more back-end protocols are
used to satisfy user requests. Although ibacmp supports standard
SA path record queries on the back-end, it also supports a
resolution protocol based on multicast traffic. The latter is not
usable on all fabric topologies, specifically ones that may not
have reversible paths or fabrics using torus routing. Users
should use the ib_acme utility to verify that multicast protocol
is usable before running other applications.
Conceptually, the default provider ibacmp implements an ARP like
protocol and either uses IB multicast records to construct path
record data or queries the SA directly, depending on the selected
route protocol. By default, the ibacmp provider uses and caches
SA path record queries.
Specifically, all IB endpoints join a number of multicast groups.
Multicast groups differ based on rates, mtu, sl, etc., and are
prioritized. All participating endpoints must be able to
communicate on the lowest priority multicast group. The ibacmp
assigns one or more names/addresses to each IB endpoint using the
ibacm_addr.cfg file. Clients provide source and destination names
or addresses as input to the service, and receive as output path
record data.
The service maps a client's source name/address to a local IB
endpoint. If the destination name/address is not cached locally
in the default provider, it sends a multicast request out on the
lowest priority multicast group on the local endpoint. The
request carries a list of multicast groups that the sender can
use. The recipient of the request selects the highest priority
multicast group that it can use as well and returns that
information directly to the sender. The request data is cached by
all endpoints that receive the multicast request message. The
source endpoint also caches the response and uses the multicast
group that was selected to construct or obtain path record data,
which is returned to the client.
The current implementation of the provider ibacmp has several
additional restrictions:
- The ibacmp is limited in its handling of dynamic changes. ibacm
must be stopped and restarted if a cluster is reconfigured.
- Support for IPv6 has not been verified.
- The number of multicast groups that an endpoint can support is
limited to 2.
The ibacmp contains several internal caches. These include caches
for GID and LID destination addresses. These caches can be
optionally preloaded. ibacm supports the OpenSM dump_pr plugin
"full" PathRecord format which is used to preload these caches.
The file format is specified in the ibacm_opts.cfg file via the
route_preload setting which should be set to full_opensm_v1 for
this file format. Default format is none which does not preload
these caches. See dump_pr.notes.txt in dump_pr for more
information on the full_opensm_v1 file format and how to configure
OpenSM to generate this file.
Additionally, the name, IPv4, and IPv6 caches can be be preloaded
by using the addr_preload option. The default is none which does
not preload these caches. To preload these caches, set this option
to acm_hosts and configure the addr_data_file appropriately.
ibacm(7), ib_acme(1), rdma_cm(7)
This page is part of the rdma-core (RDMA Core Userspace Libraries
and Daemons) project. Information about the project can be found
at ⟨https://github.com/linux-rdma/rdma-core⟩. If you have a bug
report for this manual page, send it to
linux-rdma@vger.kernel.org. This page was obtained from the
project's upstream Git repository
⟨https://github.com/linux-rdma/rdma-core.git⟩ on 2025-08-11. (At
that time, the date of the most recent commit that was found in
the repository was 2025-08-04.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
ibacm 2014-06-16 ibacm(8)
Pages that refer to this page: ib_acme(1), ibacm(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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