Van: Rick Macklem <rick.mack...@gmail.com> Datum: woensdag, 19 februari 2025 23:40 Aan: FreeBSD CURRENT <freebsd-current@freebsd.org> CC: Gleb Smirnoff <gleb...@glebi.us> Onderwerp: RFC: mount_nfs failure due to dns not running yet
Hi, The subject line basically describes the problem glebius@ ran into. When doing an NFS mount in /etc/fstab, it failed since the DNS service was not yet working and, as such, the DNS lookup of the server fqdn failed, causing the mount to fail. Note that this behaviour has existed for decades. He feels this is a bug and that mount_nfs(8) should retry getaddrinfo(3) calls until success, instead of failing the mount when the first attempt fails. The problem with just retrying getaddrinfo(3) is that it could retry forever for simple failures like a typo in the server fqdn. I can see several ways this can be handled and would like feedback from others w.r.t. these alternatives. 1) Simply document this case and encourage use of host names in /etc/hosts for NFS servers along with specifying use of file before dns in nsswitch.conf. Doing this results in the mounts working whether or not DNS is working. 2) Call it a bug and patch mount_nfs(8) to retry getaddrinfo(3) until it succeeds. (I feel this would be a POLA violation, given that the current behaviour has existed for decades and for simple cases where the fqdn will never resolve the behaviour would be to hang at the mount attempt during boot unless "bg" is specified for the /etc/fstab entry.) 3) Add a new NFS mount option "retrydns=<N>", which would enable retries of getaddrinfo(3). This would avoid any POLA violation and would allow for a convenient way to document the behaviour in "man mount_nfs". 4) ??? So, what do you think is the preferred change? rick ps: I looked and the return value from getaddrinfo(3) does not appear to be useful to discern the case of "DNS service not running yet". (I think it replies EAI_FAIL for this case.)
Add the 'late' option in fstab. So DNS should be up. Assumes the NFS share is not needed during boot of course. @work we use IP addresses for NFS mounts as it is so low level in the infra that we can't assume DNS yet. And our NFS servers don't change IP address often. This has proven to be pretty robust in the past years. Regards, Ronald.
