nfsdcltrack is the NFSv4 client tracking callout program. It is not
necessary to install this program on machines that are not acting as
When a network partition is combined with a server reboot, there are
edge conditions that can cause the server to grant lock reclaims when
other clients have taken conflicting locks in the interim. A more
detailed explanation of this issue is described in RFC 3530, section
8.6.3 and in RFC 5661, section 8.4.3.
In order to prevent these problems, the server must track a small
amount of per-client information on stable storage. This program
provides the userspace piece of that functionality. When the kernel
needs to manipulate the database that stores this info, it will
execute this program to handle it.
Enable debug level logging.
Log to stderr instead of syslog.
-s storagedir, --storagedir=storage_dir
Directory where stable storage information should be kept. The
default value is /var/lib/nfs/nfsdcltrack.
nfsdcltrack requires a command for each invocation. Supported
Initialize the database. This command requires no argument.
Create a new client record (or update the timestamp on an
existing one). This command requires a hex-encoded nfs_client_id4
as an argument.
Remove a client record from the database. This command requires a
hex-encoded nfs_client_id4 as an argument.
Check to see if a nfs_client_id4 is allowed to reclaim. This
command requires a hex-encoded nfs_client_id4 as an argument.
Remove any unreclaimed client records from the database. This
command requires a epoch boot time as an argument.
The directory for stable storage information can be set via the file
/etc/nfs.conf by setting the storagedir value in the nfsdcltrack
section. For example:
storagedir = /shared/nfs/nfsdcltrack
Debuging to syslog can also be enabled by setting "debug = 1" in this
The Linux kernel NFSv4 server has historically tracked this
information on stable storage by manipulating information on the
filesystem directly, in the directory to which
/proc/fs/nfsd/nfsv4recoverydir points. If the kernel passes the
correct information, then nfsdcltrack can use it to allow a seamless
transition from the old client tracking scheme to the new one.
On a check operation, if there is no record of the client in the
database, nfsdcltrack will look to see if the
NFSDCLTRACK_LEGACY_RECDIR environment variable is set. If it is, then
it will fetch that value and see if a directory exists by that name.
If it does, then the check operation will succeed and the directory
will be removed.
On a gracedone operation, nfsdcltrack will look to see if the
NFSDCLTRACK_LEGACY_TOPDIR environment variable is set. If it is, then
it will attempt to clean out that directory prior to exiting.
Note that this transition is one-way. If the machine subsequently
reboots back into an older kernel that does not support the
nfsdcltrack upcall then the clients will not be able to recover their