My /proc/mounts is an empty file. On Tue, Aug 1, 2017 at 4:12 PM, Rob Landley <r...@landley.net> wrote:
> On 07/31/2017 11:30 PM, Liwei Jiang wrote: > > No. I have pulled and compiled the latest code. The same problem still > > exist. It reports, "mount: '/usr/local' not in /proc/mounts" > > That's a separate error. > > Could you show me your /proc/mounts file? > > Remount needs to get the previous mount's flags from /proc/mounts. For > example, my root filesystem (ubuntu 14.04's defaults) has: > > $ grep sda1 /proc/mounts > /dev/sda1 / ext4 rw,relatime,errors=remount-ro,data=ordered 0 0 > > Without that, remount doesn't (for example) know to set the relatime > flag on the remount, and if it doesn't that flag gets removed. A remount > has to apply your current flags as an offset to the previous flags, > meaning it needs to know the previous flags. > > Way back in the dark ages mount used to maintain its own file > (/etc/mtab) with this info, but this couldn't reliably keep track of the > data: for example if you mounted or umounted anything in an overlapping > chroot, the host's /etc/mtab wouldn't get the updates. If a program ever > mounted anything with the system call instead of the mount command, > /etc/mtab wouldn't be updated. When the 'shared subtree' stuff went into > 2.6.15 mounts became a per-process attribute and a single systemwide > /etc/mtab made no _sense_ anymore. And then we built containers on top > of that combining the "in a chroot" with "per-process-attribute" and > everybody finally gave up on /etc/mtab. (I was arguing they _should_ do > so back in 2005, but nobody listened back then...) > > Since the kernel knows this information, the kernel exports it in > mtab/fstab format, so people could symlink /etc/mtab to that and always > get the right information. Newer mount commands just look for it > straight out of proc without needing the symlink. > > Rob > -- Dragonslayer
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