On 03/04/2015 05:01 PM, Tom Horsley wrote:
Here's a weird one: A system at work has (God knows why) a gazillion symlinks directly under / pointing to NFS mountpoints for filesystems (some of which might well have high latency). If I run "df -l", using the -l option in the apparently vain hope that it might not timeout forever on some NFS mount, it hangs for a long time. If I try to discover which mountpoint it hangs at by running "strace df -l", it no longer hangs. All the stat calls run fast, and df prints the info on the local filesystems. There isn't supposed to be any difference running under strace (except maybe for setuid and such), any clues what weird rabbit hole this is going down? I'm tempted to alias df to strace -o /dev/null df :-).
Methinks the "df -l" still walks down non-local filesystems but limits the _display_ to local systems. I haven't tried it, but that may be what it's doing. Odds are that while df is traversing one of those NFS beasties, it is in a "D" state (verifiable by running top and looking at it). If so, it's waiting for some sort of signal (generally "I/O Complete" which may never come if the NFS server isn't answering the bell). Since strace requires it to report what it's doing, it's getting interrupted a lot, so it doesn't hang. I mean, it's still waiting on the I/O to complete from NFS, but rather than waiting an interminate time, it's getting interrupts (signals) from strace rather than hanging on the one from the NFS system. Just a wild guess. I stay out of rabbit holes (I'm claustrophobic). ---------------------------------------------------------------------- - Rick Stevens, Systems Engineer, AllDigital ricks@xxxxxxxxxxxxxx - - AIM/Skype: therps2 ICQ: 22643734 Yahoo: origrps2 - - - - If the enemy's in range...so are you! - ---------------------------------------------------------------------- -- users mailing list users@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe or change subscription options: https://admin.fedoraproject.org/mailman/listinfo/users Fedora Code of Conduct: http://fedoraproject.org/code-of-conduct Guidelines: http://fedoraproject.org/wiki/Mailing_list_guidelines Have a question? Ask away: http://ask.fedoraproject.org
