[1/7] nfs.man: clarify effect of 'retry' option.

Commit Message

NeilBrown July 29, 2016, 5:03 a.m. UTC

The total timeout for a "mount" attempt to a non-responsive server
will always be a multiple of the time a single mount attempt in the
kernel takes, which for TCP defaults to about 4 minutes.

The documentation for the "retry" option seems to suggest that this can be used
to set a maximum but it really sets a time after which to stop retrying.
The total can be as much as "retry" plus the time for a single attempt.

So clarify the documentation a bit, and also note that retrans
defaults are different for UDP and TCP:
   #define NFS_DEF_UDP_RETRANS	(3)
   #define NFS_DEF_TCP_RETRANS	(2)

Reported-by: Howard Guo<[e-mail]>
Signed-off-by: NeilBrown <[e-mail]>
---
 utils/mount/nfs.man |   14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)



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Patch

diff --git a/utils/mount/nfs.man b/utils/mount/nfs.man
index e541cdc95cb1..a0f790a5961b 100644
--- a/utils/mount/nfs.man
+++ b/utils/mount/nfs.man
@@ -158,8 +158,8 @@  up to a maximum timeout length of 60 seconds.
 The number of times the NFS client retries a request before
 it attempts further recovery action. If the
 .B retrans
-option is not specified, the NFS client tries each request
-three times.
+option is not specified, the NFS client tries each UDP request
+three times and each TCP request twice.
 .IP
 The NFS client generates a "server not responding" message
 after
@@ -391,6 +391,16 @@  is 2 minutes, and the default value for background mounts is 10000 minutes
 If a value of zero is specified, the
 .BR mount (8)
 command exits immediately after the first failure.
+.IP
+Note that this only affects how many retries are made and doesn't
+affect the delay caused by each retry.  For UDP each retry takes the
+time determined by the
+.BR timeo
+and
+.BR retrans
+options, which by default will be about 7 seconds.  For TCP the
+default is 3 minutes, but system TCP connection timeouts will
+sometimes limit the timeout of each retransmission to around 2 minutes.
 .TP 1.5i
 .BI sec= flavors
 A colon-separated list of one or more security flavors to use for accessing