On Nov 18, 2015, at 9:49 PM, Devin Reade <gdr at gno.org> wrote:> > The one thing I would point out regarding the above link is that despite > conventional UNIX wisdom, *don't* put /usr on a separate filesystem > in CentOS 7. <sarcasm>Thank you RedHat</sarcasm> > > Flames to /dev/null.Sorry, you don?t get to throw that grenade and then run away. The old wisdom you refer to is simply obsolete, and it wasn?t Red Hat that made it so. ?Twas *progress* that made it so, specifically the fact that even a throwaway USB key has enough space to hold the complete OS on it these days. We no longer live in a world of 5 MB disk packs the size of extra large pizzas. Several OSes made /usr/{bin,lib} the same as /{bin,lib} way before Red Hat: Solaris, OS X, and Cygwin, at the least. Probably all of the embedded Linuxes, too. Even FreeBSD is starting to give up on /usr as separate from /. Although its installer still lets you put /usr into a separate slice, the boot process will break if you put it onto a different physical disk that the boot kernel can?t see, or use a different filesystem for it that isn?t compiled into the boot kernel. A truly ?traditional? Unix OS wouldn?t have this problem: as long as the tools necessary to mount /usr are in /, it would be able to boot. If you disbelieve that, try installing FreeBSD 9.0 (i.e. pre-ZFS-boot) into a VM, then move /usr into a ZFS pool. It won?t even boot into single-user mode! Ask me how I know.
On Nov 19, 2015, at 11:54 AM, Warren Young <wyml at etr-usa.com> wrote:> > Several OSes made /usr/{bin,lib} the same as /{bin,lib} way before Red Hat: Solaris, OS X, and Cygwin, at the least.Small correction: OS X doesn?t symlink /{bin,lib} to /usr/{bin,lib} as Solaris, EL7, and Cygwin do, but the installer doesn?t offer the option to put it onto a separate volume/partition, and I doubt the OS would boot if you did later move it.
--On Thursday, November 19, 2015 11:54:19 AM -0700 Warren Young <wyml at etr-usa.com> wrote:> ?Twas *progress* that made it so, specifically the fact > that even a throwaway USB key has enough space to hold the complete OS on > it these days.For the record, size of the disk was never the original motivation for keeping / separate, at least within my memory; it was to minimize the amount of disk space that needed to be fsck'd before bringing the system to single user mode without needing to revert to "rescue media" (at that time, the 125MB tape on which the OS was shipped). Even in the days of SunOS 3 (that's SunOS, not Solaris) I was installing the entire OS on one physical drive, partitioned. Sure, NFS and USENET servers had many drives, but most machines were single drives. Beyond that, I don't really want to get into a flame war on stuff that has been hashed through before. The main message is that while CentOS 6 and before *could* have / and /usr on different filesystems, don't do it with CentOS 7 per <https://access.redhat.com/solutions/53005> (paywalled). TL;DR: you'll have trouble booting some configurations including those using iSCSI. Devin
On Thu, November 19, 2015 4:49 pm, Devin Reade wrote:> --On Thursday, November 19, 2015 11:54:19 AM -0700 Warren Young > <wyml at etr-usa.com> wrote: > >> ?Twas *progress* that made it so, specifically the fact >> that even a throwaway USB key has enough space to hold the complete OS >> on >> it these days. > > For the record, size of the disk was never the original motivation for > keeping / separate, at least within my memory; it was to minimize the > amount of disk space that needed to be fsck'd before bringing the system > to single user mode without needing to revert to "rescue media"Not only. Separation of / /var /usr /home (/var/mail, ...) also was a protection from local user [accidental] denial of service attack by preventing him from filling up or running out of inodes these filesystems. Valeri> (at > that time, the 125MB tape on which the OS was shipped). Even in the days > of > SunOS 3 (that's SunOS, not Solaris) I was installing the entire OS on > one physical drive, partitioned. Sure, NFS and USENET servers had many > drives, but most machines were single drives. > > Beyond that, I don't really want to get into a flame war on stuff > that has been hashed through before. > > The main message is that while CentOS 6 and before *could* have > / and /usr on different filesystems, don't do it with CentOS 7 > per <https://access.redhat.com/solutions/53005> (paywalled). > TL;DR: you'll have trouble booting some configurations including > those using iSCSI. > > Devin > > _______________________________________________ > CentOS mailing list > CentOS at centos.org > https://lists.centos.org/mailman/listinfo/centos >++++++++++++++++++++++++++++++++++++++++ Valeri Galtsev Sr System Administrator Department of Astronomy and Astrophysics Kavli Institute for Cosmological Physics University of Chicago Phone: 773-702-4247 ++++++++++++++++++++++++++++++++++++++++
On Nov 19, 2015, at 3:49 PM, Devin Reade <gdr at gno.org> wrote:> > size of the disk was never the original motivation for > keeping / separate, at least within my memoryPrior to SysV, the location of user home directories was not standardized, and AT&T recommended that you put them in /usr.[1] Also, in the PDP days, you had things like the RL and RK series drives, which started at 2.5 MB. If you were well-heeled, you might have several of these, getting you up into the tens of megs. Thus, it made sense to put one major filesystem on each disk, like /, /usr, and /var for a 3-drive system.> it was to minimize the > amount of disk space that needed to be fsck'd before bringing the system > to single user modeThat may have been a happy side benefit, but I?ve never read such a thing in a quarter century of using Unix. Reference?> Even in the days of > SunOS 3 (that's SunOS, not Solaris) I was installing the entire OS on > one physical drive, partitioned.Unix goes back about 15 years before the advent of the Sun-3. Being fairly high-end boxes of the time, they likely would have had HDDs in the hundreds of megs range, possibly even the single-digit gigs, plenty for a complete 4.2BSD install. This was also the time in computing history where diskless or small-disk workstations were common, which gives another reason to make /usr separate: get an NFS stack up via RARP or the small local system drive, then attach to a server?s disk to complete the boot process.> The main message is that while CentOS 6 and before *could* have > / and /usr on different filesystems, don't do it with CentOS 7 > per <https://access.redhat.com/solutions/53005> (paywalled).I don?t need to pierce the paywall to know it?s a bad idea. This is enough of a clue: $ ls -l /bin lrwxrwxrwx. 1 root root 7 Jul 7 2014 /bin -> usr/bin [1]: See page 4-8 in the SVR3.2 sysadmin?s guide: http://goo.gl/E9quko