nfsdcltrack - NFSv4 Client Tracking Callout Program
nfsdcltrack [-d] [-f] [-s stable storage dir] <command> <args...>
nfsdcltrack is the NFSv4 client tracking callout program. It is not necessary
to install this program on machines that are not acting as NFSv4 servers.
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
- -d, --debug
Enable debug level logging.
- -f, --foreground
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 commands
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
by setting the
value in the
section. For example:
storagedir = /shared/nfs/nfsdcltrack
Debuging to syslog can also be enabled by setting "debug = 1" in this file.
LEGACY TRANSITION MECHANISM
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 state.
This program requires a kernel that supports the nfsdcltrack usermodehelper
upcall. This support was first added to mainline kernels in 3.8.
nfsdcltrack was developed by Jeff Layton <email@example.com