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== Summary == | == Summary == | ||
Provide a way of mounting | Provide a simple way of mounting almost the entire system read-only and share it between multiple hosts to save maintenance and space. Instead of spreading RPM package content all over the place in the filesystem, and artificially separate /bin from /usr/bin and /lib from /usr/lib, move all content to /usr and provide only symlinks in the root filesystem. | ||
/usr on its own filesystem is useful in custom setups. But instead of the Unix way to (almost randomly) split-off tools from /usr and put them in /, and require more and more tools to move to /, we | /usr on its own filesystem is useful in custom setups. But instead of the Unix way to (almost randomly) split-off tools from /usr and put them in /, and require more and more tools to move to /, we already mount /usr from inside the initramfs, to be available before the real 'init' starts. What /bin and /lib was for UNIX is the initramfs for Linux. The split of the root filesystem an /usr serves no purpose in Linux anymore and only complicates or prevents simple and more flexible setups. | ||
== Owner == | == Owner == | ||
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This new /usr could be mounted read-only by default, while the rootfs is read-write and contains only empty mount points, compat-symlinks to /usr and the host-specific data like /etc, /root, /srv. Compared to today's setups, the rootfs will be very small. The new /usr could also easily be shared read-only across several systems, and it would contain almost the entire system. Such setups are more efficient, can optionally provide a lot more security, are more flexible, provide more sane options for custom setups, and are much simpler to setup and maintain. | This new /usr could be mounted read-only by default, while the rootfs is read-write and contains only empty mount points, compat-symlinks to /usr and the host-specific data like /etc, /root, /srv. Compared to today's setups, the rootfs will be very small. The new /usr could also easily be shared read-only across several systems, and it would contain almost the entire system. Such setups are more efficient, can optionally provide a lot more security, are more flexible, provide more sane options for custom setups, and are much simpler to setup and maintain. | ||
This leaves us with the following well-defined directories, which compose the base of the system: | |||
* / | * /usr - installed system; shareable; possibly read-only | ||
* / | * /etc - config data; non-shareable | ||
* / | * /var - persistent data; non-shareable; | ||
* /run - volatile data; non-shareable; mandatory tmpfs filesystem | |||
* / | |||
In the process of moving /bin and /sbin to /usr/bin, /usr/sbin can be moved also to /usr/bin. | In the process of moving /bin and /sbin to /usr/bin, /usr/sbin can be moved also to /usr/bin. | ||
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== Roadmap == | == Roadmap == | ||
=== Phase 1 ([[Releases/ | === Phase 1 ([[Releases/17 | Fedora 17 ]] ?) === | ||
* update rpmlint | * update rpmlint | ||
* begin changing rpm packages with files in /bin, /sbin, /usr/sbin, /lib, /lib64 | * begin changing rpm packages with files in /bin, /sbin, /usr/sbin, /lib, /lib64 | ||
* | * make backward compat symlinks in %post and %ghost those symlinks | ||
* on new installation: create symlinks /bin -> usr/bin, /sbin -> usr/bin, /lib -> usr/lib, /lib64 -> usr/lib64, /usr/sbin -> bin | |||
* RPM | * RPM: 257 packages that install files in the root filesystem. | ||
* change selinux policies | * change selinux policies | ||
* prepare dracut to mount /usr from /etc/fstab | * prepare dracut to mount /usr from /etc/fstab | ||
* drop consolehelper to enable the /usr/sbin -> /usr/bin move | * drop consolehelper to enable the /usr/sbin -> /usr/bin move | ||
== Contingency Plan == | == Contingency Plan == | ||
<!-- If you cannot complete your feature by the final development freeze, what is the backup plan? This might be as simple as "None necessary, revert to previous release behaviour." Or it might not. If you feature is not completed in time we want to assure others that other parts of Fedora will not be in jeopardy. --> | <!-- If you cannot complete your feature by the final development freeze, what is the backup plan? This might be as simple as "None necessary, revert to previous release behaviour." Or it might not. If you feature is not completed in time we want to assure others that other parts of Fedora will not be in jeopardy. --> | ||
* | * We do not support to bootup with an empty /usr today, so moving things to /usr and have compat links in the rootfs should be low risk. If things turn out to get difficult, we can delay the creation of the /bin /sbin /lib lib64 compat links to a later release. | ||
== Documentation == | == Documentation == | ||
Revision as of 17:15, 21 September 2011
Move all to /usr
Summary
Provide a simple way of mounting almost the entire system read-only and share it between multiple hosts to save maintenance and space. Instead of spreading RPM package content all over the place in the filesystem, and artificially separate /bin from /usr/bin and /lib from /usr/lib, move all content to /usr and provide only symlinks in the root filesystem.
/usr on its own filesystem is useful in custom setups. But instead of the Unix way to (almost randomly) split-off tools from /usr and put them in /, and require more and more tools to move to /, we already mount /usr from inside the initramfs, to be available before the real 'init' starts. What /bin and /lib was for UNIX is the initramfs for Linux. The split of the root filesystem an /usr serves no purpose in Linux anymore and only complicates or prevents simple and more flexible setups.
Owner
- Name: Harald Hoyer
- Email: harald@redhat.com
Current status
- Targeted release: Fedora 16
- Targeted release: Fedora 17
- Last updated: (DATE)
- Percentage of completion: 0%
Detailed Description
There is no way to reliably bring up a modern system with an empty /usr, there are two alternatives to fix it: copy /usr back to the rootfs or use an initramfs which can hide the split-off from the system.
Historically /bin, /sbin, /lib had the purpose to contain the utilities to mount /usr. This role can now be taken by the initramfs. Because the initramfs knows, where to find the root partition (which includes /etc), it can parse /etc/fstab and other configuration files and mount /usr before it finally switches the root partition and executes /usr/bin/init. From this point on init mounts the remaining partitions in /etc/fstab and the system starts as usual.
The long-term plan is to clean up the mess and confusion the current split of / vs. /usr has created. All tools will move back to /usr where they belong, and the rootfs will only contain compat-symlinks into /usr. Almost the entire system installed by packages will reside in /usr. This will split all non-host specific data to /usr. /usr can then be seen as the Unix System Resources partition (/System), which defines the base operating system (e.g. F18 or RHEL-7).
This new /usr could be mounted read-only by default, while the rootfs is read-write and contains only empty mount points, compat-symlinks to /usr and the host-specific data like /etc, /root, /srv. Compared to today's setups, the rootfs will be very small. The new /usr could also easily be shared read-only across several systems, and it would contain almost the entire system. Such setups are more efficient, can optionally provide a lot more security, are more flexible, provide more sane options for custom setups, and are much simpler to setup and maintain.
This leaves us with the following well-defined directories, which compose the base of the system:
- /usr - installed system; shareable; possibly read-only
- /etc - config data; non-shareable
- /var - persistent data; non-shareable;
- /run - volatile data; non-shareable; mandatory tmpfs filesystem
In the process of moving /bin and /sbin to /usr/bin, /usr/sbin can be moved also to /usr/bin.
Example F15
This output is from a modified F15 standard installation:
# df -h Filesystem Size Used Avail Use% Mounted on rootfs 2.0G 162M 1.8G 9% / udev 484M 0 484M 0% /dev tmpfs 494M 248K 493M 1% /dev/shm tmpfs 494M 43M 451M 9% /run /dev/sda2 2.0G 162M 1.8G 9% / /dev/sda5 13G 3.3G 8.8G 28% /usr tmpfs 494M 43M 451M 9% /run tmpfs 494M 0 494M 0% /sys/fs/cgroup tmpfs 494M 0 494M 0% /media /dev/sda1 117M 47M 65M 42% /boot
# ls -l / total 66 lrwxrwxrwx 1 root root 7 Jul 7 16:28 bin -> usr/bin dr-xr-xr-x. 5 root root 1024 Jul 4 19:33 boot drwxr-xr-x 16 root root 3480 Jul 11 19:34 dev drwxr-xr-x. 127 root root 12288 Jul 11 19:34 etc drwxr-xr-x. 3 root root 4096 Jul 4 17:33 home lrwxrwxrwx 1 root root 7 Jul 11 17:30 lib -> usr/lib lrwxrwxrwx 1 root root 9 Jul 11 17:23 lib64 -> usr/lib64 drwx------. 2 root root 16384 Jul 4 16:02 lost+found drwxr-xr-x 2 root root 40 Jul 11 19:33 media drwxr-xr-x. 2 root root 4096 May 18 13:33 mnt drwxr-xr-x. 2 root root 4096 May 18 13:33 opt dr-xr-xr-x 116 root root 0 Jul 11 17:33 proc dr-xr-x---. 6 root root 4096 Jul 11 15:58 root drwxr-xr-x 28 root root 1060 Jul 11 19:35 run lrwxrwxrwx 1 root root 7 Jul 7 16:28 sbin -> usr/bin drwxr-xr-x. 2 root root 4096 Jul 4 16:02 selinux drwxr-xr-x. 2 root root 4096 May 18 13:33 srv drwxr-xr-x 13 root root 0 Jul 11 19:33 sys drwxrwxrwt. 14 root root 4096 Jul 11 19:34 tmp drwxr-xr-x. 13 root root 4096 Jul 4 19:55 usr drwxr-xr-x. 18 root root 4096 Jul 4 17:27 var
Benefit to Fedora
Clear separation of operating system and host specific resources. /usr can be read-only and shareable.
Scope
The ability to share /usr is especially useful for clusters and virtual machines. The ability to mount /usr read-only (e.g. on read-only media) adds to the security of the machine.
How To Test
User Experience
- less toplevel directories
Dependencies
- initramfs (dracut)
- changes in selinux policies
- repackaging of packages with content in /bin, /sbin, /lib*
- drop consolehelper to move /usr/sbin/* to /usr/bin
- alternatives symlinks?
- filesystem rpm, toplevel symlinks
Roadmap
Phase 1 ( Fedora 17 ?)
- update rpmlint
- begin changing rpm packages with files in /bin, /sbin, /usr/sbin, /lib, /lib64
- make backward compat symlinks in %post and %ghost those symlinks
- on new installation: create symlinks /bin -> usr/bin, /sbin -> usr/bin, /lib -> usr/lib, /lib64 -> usr/lib64, /usr/sbin -> bin
- RPM: 257 packages that install files in the root filesystem.
- change selinux policies
- prepare dracut to mount /usr from /etc/fstab
- drop consolehelper to enable the /usr/sbin -> /usr/bin move
Contingency Plan
- We do not support to bootup with an empty /usr today, so moving things to /usr and have compat links in the rootfs should be low risk. If things turn out to get difficult, we can delay the creation of the /bin /sbin /lib lib64 compat links to a later release.