Use an FHS 3.0 compliant pidpath

[brianhlin]

https://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard#FHS_compliance

Modern Linux distributions include a /run directory as a temporary
filesystem (tmpfs) which stores volatile runtime data, following the
FHS version 3.0. According to the FHS version 2.3, this data should be
stored in /var/run but this was a problem in some cases because this
directory isn't always available at early boot. As a result, these
programs have had to resort to trickery, such as using /dev/.udev,
/dev/.mdadm, /dev/.systemd or /dev/.mount directories, even though the
device directory isn't intended for such data. Among other advantages,
this makes the system easier to use normally with the root filesystem
mounted read-only.

[simonmichal]

@brianhlin : thanks for the PR! However, I do see few issues :

• the /run/xrootd directory is not packaged correctly, in the spec file we still have:
  

  xrootd/packaging/rhel/xrootd.spec.in

  Line 524 in ced832b

  mkdir -p $RPM_BUILD_ROOT%{_var}/run/xrootd

  
  

  xrootd/packaging/rhel/xrootd.spec.in

  Line 743 in ced832b

  %attr(-,xrootd,xrootd) %dir %{_var}/run/xrootd

  
  so need to replace %{_var}/run with %{_rundir}

• also, we need to still suport rhel6, so your changes need to be conditional and e.g. for slc6 we need to keep /var/run

Could you please update the PR?

[brianhlin]

Looking at this again, RHEL7 appears to symlink /var/run to /run so I don't think this change is strictly necessary