Hi Michael, The man page looks good to me. A few comments are inline. On Sat, Apr 04, 2020 at 01:08:50PM +0200, Michael Kerrisk (man-pages) wrote: > Hello Dmitry, Andrei, et al. > > I have written a manual page to document time namespaces. > Could you please take a look and let me know of any > corrections, improvements, etc. > > The rendered page is shown below. Th epage source is at the foot of > this mail. > > Thanks, > > Michael > > > NAME > time_namespaces - overview of Linux time namespaces > > DESCRIPTION > Time namespaces virtualize the values of two system clocks: > > · CLOCK_MONOTONIC (and likewise CLOCK_MONOTONIC_COARSE and > CLOCK_MONOTONIC_RAW), a nonsettable clock that represents mono‐ > tonic time since—as described by POSIX—"some unspecified > point in the past". > > · CLOCK_BOOTTIME (and likewise CLOCK_BOOTTIME_ALARM), a clock that > is identical to CLOCK_MONOTONIC, except that it also includes > any time that the system is suspended. > > Thus, the processes in a time namespace share per-namespace values > for these clocks. This affects various APIs that measure against > these clocks, including: clock_nanosleep(2), nanosleep(2), > clock_gettime(2), and /proc/uptime. timer_settime, timerfd_settime > > Currently, the only way to create a time namespace is by calling > unshare(2) with the CLONE_NEWTIME flag. This call creates a new > time namespace but does not place the calling process in the new > namespace. Instead, the calling process's subsequently created > children are placed in the new namespace. This allows clock off‐ > sets (see below) for the new namespace to be set before the first > process is placed in the namespace. The > /proc/[pid]/ns/time_for_children symbolic link shows the time > namespace in which the children of a process will be created. We can mention that the current process can enter the namespace if it call setns on /proc/self/ns/time_for_children. > > /proc/PID/timens_offsets > Associated with each time namespace are offsets, expressed with > respect to the initial time namespace, that define the values of > the monotonic and boot clocks in that namespace. These offsets > are exposed via the file /proc/PID/timens_offsets. Within this > file, the offsets are expressed as lines consisting of three > space-delimited fields: > > <clock-id> <offset-secs> <offset-nanosecs> > > The clock-id identifies the clock whose offsets are being shown. > This field is either 1, for CLOCK_MONOTONIC, or 7, for CLOCK_BOOT‐ > TIME. The remaining fields express the offset (seconds plus > nanoseconds) for the clock in this time namespace. These offsets > are expressed relative to the clock values in the initial time > namespace. In the initial time namespace, the contents of this > file are as follows: I think we can mention that offset-secs can be negative, but offset-nanosleep has to be 0 or positive. Thanks, Andrei
