Filesystem Standard Group Daniel Quinlan draft submitted: 93/10/17 quinlan@bucknell.edu Advance Draft on Linux Filesystem Structure Status of this draft This draft is being distributed to the members of the Linux community in order to solicit their reactions to the array of ideas, concepts, and proposals included within it. While the entire content of the draft may not meet everyone's individual approval, they may be a good beginning to solving many problems. This draft is the product of the Filesystem Standard (FSSTND) unit of the linux-activists@Niksula.hut.fi mailing list. This draft is a working document of the Filesystem Standard channel, the author, and all other groups collaborating to help create this draft. The distribution of this draft is limited at this time to those directly involved in its development. ------------------------------------------------------------------------ ABSTRACT This document is an extensive undertaking to correct outstanding problems with the de-facto filesystem standard in use by developers, programmers, administrators, and users. Our purpose and goal is to produce a draft of exceptional quality that developers and others will voluntarily adopt to solve well acknowledged problems. The FSSTND group hopes that this draft will be eventually adopted as a better standard than the de-facto standard produced by the current disarray of ideas. We felt that it was desirable to first call attention to some of the fundamental problems with the current filesystem situation: (1) There is no single well-accepted Linux directory structure. Instead, there are many different ones, each being incompatible with each other, this is a problem that justifies our effort. (2) In the most widely used filesystem hierarchies, the directories are not well structured and differ gratuitously from more modern standards. (3) The current layout is confusing for new users and equally unsettling in nature for well-experienced Unix users. (4) The incompatibilities between primary installation packages and other software packages are typically solved by methods of a less than appealing nature. (5) Overall, symbolic links are used too often within the filesystem to fix problems. However, there are times when symbolic links need to be used to ensure backward compatibility or to allow specific systems to have an individual filesystem structure. The FSSTND group seeks to correct these problems by proposing a good filesystem structure that the Linux community may voluntarily follow. While developing this draft, approval and input was received from a number of Linux developers, noted Linux programmers, many system administrators, and both experienced and novice users. For this reason, I feel that following our recommendations is a good thing. If you feel that there is a problem with this effort or the substance of the draft, please first contact the draft coordinator, Daniel Quinlan , with your comments. ------------------------------------------------------------------------ SPECIFIC PROBLEMS Naturally, while defining a Linux filesystem structure, there were some specific problems that we sought to correct. Here are some of the major and well-accepted ones: o Linux is not well prepared for a network installation including the possibility of a read-only /usr partition and diskless (or small local disk) workstations. o The primary binary directories, /bin and /usr/bin, do not have well defined divisions between them. The binaries that are in each path greatly differ between the various Linux installation packages. o Problems concerning /etc - Many configuration files that aren't essential appear in /etc. - Non-essential binaries, such as networking binaries, are often dumped into /etc and symbolic links applied to fix any compatibility problems - Including both binaries and configuration files in /etc makes it more confusing and harder to maintain for inexperienced users or system administrators with especially large systems. o The current implementation of /usr cannot be mounted read-only because it contains variable files and directories that need to be written to. o In a networked environment, certain filesystems contain information specific to a single machine. Therefore these filesystems cannot be shared (with NFS). While these are some of the major problems we addressed, there were numerous additional problems that needed to be solved. This draft attempts to address many of those other problems, but there may be something we missed. If you wish to bring something to our attention, please note there are some things we have discussed at length, but did not include in this draft (for good reasons). ------------------------------------------------------------------------ OBJECTIVES In trying to solve the above problems, we saw several objectives that needed to be accomplished in addition to the more technical matters. These goals comprise the correction of outstanding problems as well as the validation of our discussion and work. o Solve the above problems while also limiting the possible transition difficulties resulting from moving away from the former de-facto standards. o Gain approval of distributors, developers, and other important people in the Linux movement, as well as their suggestions. o Provide a standard that all of the Linux community would choose to follow because it will solve the above problems as well as provide the most sensible structure for Linux's filesystem. o While conformance to this or any other standard in Linux is obviously completely voluntary, we wish to impress upon developers that this organization is a very sensible way to lay out a Linux filesystem. If you, as a developer, wish to suggest any improvements, we are willing to listen. ======================================================================== THE FILESYSTEM STRUCTURE This is the root directory structure. In general, enough should be contained in root partition to boot, restore, recover, and/or repair the system. Our primary concern was to keep root as small as reasonably possible in terms of number of directories, files, and disk space. You might ask, "Why is this desirable?" o The root is often mounted from very small media. For example, most people using Linux install and do recovery by mounting root off of a RAM disk which is copied from a single 1.44M or 1.2M floppy disk. o Root has many system-specific configuration files in it, a kernel that is specific to the system, a different hostname, etc. This means that root isn't usually shareable between networked systems. Keeping root small on networked systems minimizes the amount of space lost on servers to non-shareable files. It also allows workstations with smaller local hard drives. o While you may have a large root partition, and may be able to fill it to your heart's content, there will be people with smaller partitions. If you have more files installed, you may find incompatibilities with other systems using limited root partitions. If you are a developer then you may be sharing this problem with a large number of users. No single package should have its own specific root directory. This structure provides more than enough flexibility for any package. Any package which does occupy a directory under root suffers from sheer arrogance. / : the root directory | |- bin : essential command binaries |- boot : static files of the boot loader |- dev : device files |- etc : essential system configuration |- home : user home directories |- lib : shared libraries ("libc.so.*" and "libm.so.*") |- lost+found : files and directories found by 'fsck' |- mnt : mount point of temporary partitions |- proc : process information pseudo-filesystem |- root : home directory for root |- sbin : essential system binaries |- tmp : temporary files |- usr : second major permanent mount point |- var : files that vary with time or by machine (non-configuration) \- {kernel image} Following this section, each directory is explained in full. The root directory normally contains the current kernel image. The kernel image name is locally configurable, but the name we suggest (that has been used in recent Linux kernel sources) is "vmlinux". ------------------------------------------------------------------------ /bin : essential binaries only (for use by all users) There should be no subdirectories within /bin. The /bin directory should not contain binaries that are only for use by root. All root-only binaries such as standard daemons, init, getty, mkfs, et al (previously found in /etc), shall now be placed in /sbin or /usr/sbin depending on the necessity of the command. For discussion and our definition of essential (necessity and related concepts) please read the issues and rationale section towards the end of this draft. Command binaries that are not essential enough to place into /bin should be placed into /usr/bin, instead. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . REQUIRED files for /bin: general commands: The following commands have been added because of their essential nature in the system. A few have been added because of their traditional placement in /bin. { cat, chgrp, chmod, chown, cmp, compress, cp, date, dd, df, du, ed, false, free, grep, hostname, kill, killall, ln, login, ls, mkdir, mknod, mv, od, ps, pwd, rm, rmdir, sh, stty, su, sync, test, touch, true, uncompress, uptime, w, zcat } /* possible removal: od */ networking: These are deemed the only necessary networking binaries that both root and users will want or need to execute other than the ones in /usr/bin or /usr/local/bin. { ftp, netstat, ping, telnet } /* possible removal: ftp, telnet */ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . RECOMMENDED files for /bin: These files should appear in /bin if space is not at a premium { "an interactive shell" (preferably csh), "a pager" (more or less), passwd, wall, write } . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OPTIONAL files for /bin: These may appear in /bin at the discretion of system administrators, but are in no way required and are be better placed in /usr/bin. { awk, basename, dirname, expr, head, pstree, tload, top, sed, "other login shells deemed necessary (bash, tcsh, zsh, et cetera)" } /* possible removal: awk, sed musing: tail possible move up: basename, dirname, expr (often used in sh scripts) */ ------------------------------------------------------------------------ /boot : static files of the boot loader This directory contains everything for boot except configuration files and the map installer. This includes saved master boot sectors, sector map files, and anything else that is not directly edited by hand. The boot loader program should be placed into /sbin and configuration files for boot loaders into /etc. For LILO: Old location New location ------------------------ ----------------- /etc/lilo/config.defines /etc/lilo.defines /etc/lilo/config /etc/lilo.conf /etc/lilo/disktab /etc/disktab /etc/lilo/lilo /sbin/lilo /etc/lilo/boot.NNNN /boot/boot.NNNN /etc/lilo/part.NNNN /boot/part.NNNN /etc/lilo/map /boot/map /etc/lilo/*.b /boot/*.b *.b are the first and second stage boot loader, plus all those chain loaders. QuickInst (if used at all) should be placed into /usr/sbin and the activate command is left out of this scheme because its future is uncertain at this time. Extra kernel images should be stored in /boot. The main kernel can either be placed in / or in /boot according to personal preference. If placed in /, the kernel may possibly be a symlink to a kernel image in /boot. ------------------------------------------------------------------------ /dev : Device files There are no subdirectories within /dev. /dev usually also contains a file, MAKEDEV, a shell script designed to create devices as needed. It also often contains a MAKEDEV.local for any local-only devices. Symbolic links within /dev "to make it easier to understand" are dangerous and not a good idea. The largest problem with symlinks in /dev is that they are often not updated when other devices are. If you feel you absolutely must create links in /dev then use hard links, and not symbolic ones. A good standard already exists for Linux devices. We believe that the current standard should by followed in all cases. The device list is maintained by Rick Miller , the Linux Device Registrar. /* where is the device standard stored? */ ------------------------------------------------------------------------ /etc : Essential system configuration files No binaries or subdirectories should go directly into /etc. Commands which would have in the past been found in /etc should now be placed in /sbin. This includes such commands as init, getty, and update. Binaries such as hostname which are used by users as well as root should not be placed in /sbin, but in /bin. REQUIRED files for /etc: { adjtime, fdprm, fstab, group, initttab, issue, magic, motd, mtab, mtools, passwd, printcap, profile, protocols, rc*, securetty, services, shells, termcap, utmp } networking REQUIRED files (if networking is installed): { ftpusers, host, host.conf, hosts.equiv, networks } There may be more configuration files than just these, but some that are not essential should be placed in /usr/etc rather than /etc. ------------------------------------------------------------------------ /home : User home directories /home is a fairly standard concept, but it is clearly a site-specific filesystem. The setup will differ from machine to machine. On small systems, each user's directory is typically one of the many subdirectories of /home ("/home/jane", "/home/bill", "/home/xavier", et cetera). On large systems (especially when the /home directories are mounted across a number of machines using NFS) it is a good idea to subdivide user home directories. Subdivision can be accomplished by using subdirectories such as /home/staff, /home/guests, /home/students, et cetera. Different people prefer to place user accounts in a variety of places and because of this reason, no programming should rely on this location. If you want to find out a user's home directory, you should use the field in /etc/passwd or another reliable method (I know of no other reliable methods). ------------------------------------------------------------------------ /lib : Shared libraries (needed to run dynamically linked binaries) Only the shared library images necessary to boot the system should be placed in /lib. The shared library images are "/lib/libc.so.*" and "/lib/libm.so.*" and not the actual ".a" files. XFree86 libraries do not belong in /lib. Essentially, only the dynamic shared libraries needed to run programs in /bin and /sbin should be here. A single symbolic link for gcc currently exists in /lib pointing "/lib/cpp -> /usr/lib/gcc-lib/i-?86-linux/2.4.?/cpp". No binaries should be added to /lib in addition to cpp. ------------------------------------------------------------------------ /mnt : Mount point for temporarily mounted filesystems This is the location where the system administrator may temporarily mount filesystems as needed. The setup of this directory is a local issue and should not affect the way any program is run. ------------------------------------------------------------------------ /proc : Proc based process system The procps filesystem is becoming the standard Linux method for handling process information rather than /dev/kmem and other nasty methods. This is only recommended, but should in time become the standard for the storage and retrieval of process information as well as other kernel and memory information. ------------------------------------------------------------------------ /sbin : System binaries (binaries once kept in /etc) Utilities used for system administration (and other root-only commands) are stored in /sbin, /usr/sbin, and /usr/local/sbin. /sbin typically contains files essential for the booting phase of starting the system up. Any non-essential commands should be placed into /usr/sbin. Local-only system administration stuff should now be placed into /usr/local/sbin. The concept of what goes into "sbin" directories is simple. If a user will need to run it, then it should go somewhere else. If it will only be run by root (i.e. system administration commands, networking daemons, system startup), then it should go in /sbin (or in /usr/sbin if the item is not essential). Files such as 'chfn' and 'ac' which users only occasionally use should still be placed in /usr/bin. 'ping', although it is absolutely necessary for root (network recovery and diagnosis) is often used by users and should live in /bin for that reason. Let me state it one more time, if there is any chance at all that a user should need to run it, do not put it here! Users should never have to place /sbin (or any of the 'sbin' directories) in their path. It is true that they should probably not even be able to execute anything dangerous in /sbin if you (and programmers) have done the job right. It is reasonable to want to let them see what files are in /sbin. Therefore, don't make the directory totally unreadable unless you must. /sbin was not created to protect users or to prevent them from seeing the OS, but to provide a good division between binaries everyone uses and commands that *only* administrators use (99.9% of the time). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . REQUIRED files for /sbin: general: { getty, init, update, mkswap, swapon, swapoff } shutdown commands: { halt, reboot, shutdown } filesystem commands: { fsck, fsck.*, tunefs, mkfs, mkfs.*, mount, umount } networking: { ifconfig, route } . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . /sbin is traditionally known for statically linked files although as you can see we have not even mentioned linking anything statically yet. This is because we feel that the need for statically linked files is not great except in several cases: RECOMMENDED to be linked statically: ln, sync Yes, neither 'ln' or 'sync' are normally placed in /sbin. If the version of 'ln' and 'sync' that you possess are not a reduced (in functionality or interface) version of the normal commands then they should just replace the ones in /bin. If either is a reduced version that only offers minimal features then it should be kept separately in /sbin so that users do not have to use a reduced functionality command. ======================================================================== /usr : Second major mount point (permanent) | |- X11 : The X windows directory version 11 |- bin : Most user commands |- dict : Spelling dictionaries |- doc : Miscellaneous documentation |- etc : Other configuration files (for programs in /usr/bin) |- g++-include : GNU C++ include files |- games : Games and educational binaries |- include : Header files included by C programs |- info : The GNU info documentation system's primary directory |- lib : Libraries |- local : Local directory (empty after main installation) |- man : Online manuals |- sbin : Non-essential system administration binaries \- src : Source code X11 is possibly a symlink to /usr/X386 or something else. The following list of directory symbolic links need to be added. This only needs to be done until compatibility with the /var scheme can be assumed to exist. /usr/adm -> /var/adm /usr/preserve -> /var/preserve /usr/spool -> /var/spool /usr/tmp -> /var/tmp Most of the above symlinks should in time become unneeded as packages are changed to support /var in addition to /usr. The GNU Emacs lock file directory, if Emacs is installed, should be a symlink pointing to /var/lock/emacs if you want to be able to mount /usr read-only. It is usually found in /usr/emacs, /usr/lib/emacs, or /usr/local/lib/emacs. ------------------------------------------------------------------------ /usr/X11 : X386 X11 installation directory |- bin |- doc |- include |- lib \- man This hierarchy is reserved for the use of XFree86 X11 releases. In order to simplify matters and make X386 more compatible with other X11 packages from XFree86, our recommendation is to place a symbolic link, /usr/X11 pointing to /usr/X386 (or whatever directory your X11 package was compiled to utilize). ------------------------------------------------------------------------ /usr/etc : Non-essential system configuration files All non-essential system configuration should be placed in here. Basically, files placed in here will be configuration for files in /usr/bin or /usr/sbin. ------------------------------------------------------------------------ /usr/lib : Libraries for programming and packages |- emacs : Support files for the GNU Emacs editor |- groff : Libaries/directories for the GNU groff system |- gcc-lib : System specific files/directories for GNU C compiler |- terminfo : Directories for terminfo database |- uucp : Commands for uucp \- zoneinfo : Timezone information and configuration The word, library, includes static data files and some internal binaries as well. ------------------------------------------------------------------------ /usr/local : Local directory |- bin : Local only binaries |- etc : Configuration for local only binaries |- games : Locally installed games |- lib : Libraries for /usr/local |- info : Local info pages |- man : Man page hierarchy for /usr/local |- sbin : Local only system administration \- src : Local source code This should be 100% empty after installing Linux, no exceptions other than the listed _empty_ directory stubs. Let me spell it out for the concept impaired, "E M P T Y". It should also be untouched during system upgrades. Locally installed software should be placed within /usr/local rather than /usr *unless* it is being installed to replace or upgrade software in /usr *or* it is felt that the installed software is "important enough" to place in /usr or in /. ------------------------------------------------------------------------ /usr/man : Manual page hierarchy |- man1 : User programs |- man2 : System calls |- man3 : Library functions and subroutines |- man4 : Devices |- man5 : File formats |- man6 : Games |- man7 : Miscellaneous |- man8 : System Administration \- man9 : Kernel internal variables and functions The cat page sections (cat[1-9]) containing formatted manual page entries are also found within subdirectories of /usr/man, but are not required nor should they be distributed in lieu of nroff source manual pages. Local manual pages should be stored in /usr/local/man which contains a similar directory structure (man[1-8], empty subdirectories can be omitted). X Windows manual pages should be stored in /usr/X11/man in an identical directory structure (man[1-8], empty subdirectories can be omitted). As Linux (and Unix) is further utilized in foreign countries and manual pages are translated to non-English versions, there is the impending problem that these manual pages will have to be stored somewhere else. Some German releases of Linux have already created a manual page system that is placed in /usr/man with the suffix "g". This is a poor solution and will cause further problems in the long run as other langauges appear, especially other langauges starting with the same letter (Gaelic, Greek, whatever). Therefore, all non-English manual pages sections should be stored in subdirectories within /usr/man named according to the language that the the contained manual pages are written in (lowercase characters), hence, for the German manual pages: /usr/man/german/man[1-9] and possibly /usr/man/german/cat[1-9] Then, German-speaking Linux users can add /usr/man/german to their MANPATH before /usr/man so that /usr/man/german manual pages are referenced first. If a German manual page is not found for a given command then the English version may be referenced. This setup will be needed as the number of foreign (non-English) manual pages increases. German is the language mentioned here since it is the only non-English manual page system distributed with any Linux system at this time. Other languages will probably follow and they should follow this scheme as well. The practice of placing non-English in subdirectories of /usr/man should be followed as well for other manual page hierarchies, such as /usr/local/man and /usr/X11/man. Using the language itself (/usr/man/deutsch) rather than the English (/usr/man/german) was strongly considered, but this was met with disapproval from many people, including those who do not speak English as a first language. Reasons: simplicity, the difficulty in displaying many languages' names in 7 bit characters, and the fact that everyone can hopefully recognize what their language is in English. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A description of each section follows: man1: User programs Manual pages that describe publicly accessible commands are contained in this chapter. Most program documentation that a user will need to use is located here. man2: System calls This section describes all of the system calls which are entries to the Linux kernel (operating system). This section can be very useful to programmers, but users have little need of the items in section 2. man3: Library functions and subroutines Section 3 describes user-level library routines. This is another chapter that is only really of interest to programmers. man4: Special files Section 4 describes the special files, related driver functions, and networking support available in the system. Typically, the device files found in /dev. man5: File formats The formats for many nonintuitive data files are documented in the section 5. This includes various include files, program output files, and system files man6: Games This chapter documents games, demos, and generally trivial programs. Different people have various notions about how essential this is. man7: Miscellaneous Manual pages that are difficult to classify are designated as being section 7. The *roff and other text processing macro packages are found here. man8: System administration Documentation for programs used by system administrators for system operation and maintenance are documented here. Some of these programs are also occasionally useful for normal users. man9: Kernel internal variables and functions This appears on Linux systems to document the kernel source code. ------------------------------------------------------------------------ /usr/sbin : Non-essential standard system binaries Any non-essential system administration binaries, non-essential networking daemons (most other than those mentioned to be in /sbin), large system administration tools, interface programs, or anything used only by the sysadmin that isn't essential. Local system binaries and local administration shell scripts belong in /usr/local/sbin. ------------------------------------------------------------------------ /usr/src : Source code | \- linux : Source code for Linus' kernel Any non-local source code should be placed in this subdirectory, the only thing in /usr/src that should always be placed in a certain location is the kernel source (when present or linked in part to the /usr/include structure). [ Author's note: Also, if you have any taste, you'll learn to use subdirectories. ] The source code for the kernel should always be in place or at least the include files from the kernel source. Those files are located in these directories: /usr/src/linux/include/asm /usr/src/linux/include/linux /usr/include usually contains links to 'asm' and 'linux' in the source directory, therefore, at least those include files should always be distributed with installations. They should also be distributed in the /usr/src/linux directory so there are no problems when system administrators upgrade their kernel version for the first time. ------------------------------------------------------------------------ /var : Directories of files that vary on different systems and machines |- adm : System logging and accounting files |- domain : DNS files (for named), networking only |- lock : Lock files |- preserve : Used to save text edited by 'vi' after crash or hangup |- spool : Directories for queuing work to be performed later \- tmp : Second temporary directory This directory contains the directories of all files that vary with time and is usually a local directory. These include logging files, accounting files, backup files for editors and other programs, and spool directories. The reason for a /var is to make it possible to mount /usr read-only. Everything that once went into /usr that is written to on a temporary basis, now goes into /var. The aforementioned symbolic links, also mentioned below in the issues and rationale section, should be added to /usr for compatibility. This is very helpful if you are mounting /usr through NFS or if you want a read-only /usr. ------------------------------------------------------------------------ /var/domain : DNS and named stuff |- forward \- reverse This is only needed for systems using DNS (networking protocol for name servers). /* I am hoping to add a *much* more extensive explanation after some contact is made with Linux networking developers. There is a very excellent proposal from Drew Eckhardt (that has precedence as well) that will eventually be discussed. */ ------------------------------------------------------------------------ /var/lock : Lock files |- device : Device locks \- emacs : Emacs lock files Lock files should be stored with a subdirectory of /var/lock appropriate subdirectory such as the emacs lock file directory. This directory *does not* replace older locations for lock files other than /usr/spool/uucp and the serial lock files that were contained within it. However, if you are the maintainer of a program that uses lock files and you wish to add a subdirectory for lock files within /var/lock, then it is a good idea to contact the FSSTND channel or myself to discuss placement of a directory for your lock files. If you are interested in being able to mount /usr read-only then you may wish to recompile whatever package it is that uses /usr for lock files and place them in here, again - contact me if you want to add stuff on a permanent basis (i.e. you are a developer or a programmer of a Linux package). The Emacs editor's lock files should be saved in /var/lock/emacs. It is necessary to recompile Emacs to do this or to place an appropriate symlink where the Emacs lock file directory lies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . /var/lock/device: Device lock files All lock files for devices should now be placed in /var/lock/device rather than /usr/spool/uucp or whereever they were stored in the past. ------------------------------------------------------------------------ /var/spool : Spooling directories (queue work, work to be done later) |- at : at jobs |- cron : Cron jobs |- lpd : Printer spool directory |- mail : Directory for user mailboxes |- mqueue : Outgoing mail queue \- uucp : Spool directory for uucp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . /var/spool/lpd : Printer spool direcotry |- {printer name} : Spools for a specific printer \- {printer name}.LOCK : Lock file for a specific printer ------------------------------------------------------------------------ Issues and Addtional Rationale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . What is Essential? The answer is: essential to clean, create, prepare, check, find and mount other filesystems (possibly on remote machines). There are other definitions, but this is a general definition that most people will at least incorporate into their own. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Networking Networking presented an interesting dilemma. Many people like to place networking binaries and configuration separate from other binaries and configuration. However, we disagree. We feel that networking is not a "package", but an integral part of most Unix machines. Because of this networking should not be placed into a single directory, but systematically placed in the appropriate directories. /bin : anything a user will want to use that is also considered essential (ftp, netstat, telnet, ping) /sbin : anything only root needs and is considered essential (ifconfig, route) /usr/bin : any binaries a user will want to use, but are not essential (finger, rcp, rlogin, et al.) /usr/sbin : any root only networking binaries that are not essential (networking daemons, lpd, et al.) While this may seem confusing at first (and it does take a moment to digest), it does make sense. If you can only mount root for some reason and you need access to networking to repair your system, you don't need the files to be off in /usr/etc (as they often are). Files that are needed to mount /usr in normal (and emergency situations) are placed on the root subtree and any others are placed in /usr in order to keep the size of root small. Configuration files for networking similarly go into /etc and /usr/etc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Architecture-independent Structures Many people note that in this draft, there is no /usr/share. The structure, /usr/share, typically contains architecture-independent files such as man-pages, timezone, terminfo information, et al. As of this time, there are no different architectures for Linux, but with the passage of time we should see Linux include other architectures. The reason that we do not include /usr/share in this standard is that /usr/share is very difficult to set up *without* another architecture to examine when defining the structure. Keep in mind that things commonly specified, like "/usr/share/man" are obvious . . . and wrong. After all, some manual pages (like the man pages for the devices: /usr/man/man4) will be architecture specific. In addition, there may be other files which may actually turn out to be architecture specific simply because the DBM formats are not compatible. Thus, we are going to wait on /usr/share for now. If we need /usr/share in the future, it is simple enough to put in symlinks from the current existing structure into /usr/share. So the primary directory names which programs should reference should be /usr/man, and then if appropriate certain directories in /usr/man can be symlinked to /usr/share/man. This avoid "gotcha's" like /usr/man/man4 that people will probably forget about if we try to design /usr/share without actually mapping out a NFS supported /usr that supports multiple architectures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Symbolic Links There are a wide range of uses for symbolic links (symlinks) in every filesystem. While symlinks are not encouraged for default setup (found after installing Linux) in a standard such as this, they are often used with good purpose on different systems. The point is that symlinks should be there to keep everything where everyone else expects find it Be prepared to accept that certain directories, even those contained on the root directory, are still going to be symlinks. For instance, on some systems /home will not be on the root, but symlinked to a /var directory, or to somewhere else. /home could also have its own physical partition, of course, and be mounted on its own. Similarly, because /usr might be on a central fileserver mounted via NFS, /usr/local could be symlinked to /var/local. Like /usr/emacs/lock, this change can be justified by recalling one definition of /var: "directories of files that vary on different systems and machines". Sometimes systems will also link /tmp to /var/tmp if the root partition becomes too small (or starts out too small). There are more examples of "good" uses of symbolic links, but the entire issue boils down to two things: packages should be able to find things where they expect them (within reason) and symbolic links can be used to solve the problem in many cases. However, problems also can arise from using too many symbolic links. These problems include overreliance on symbolic links to solve problems, confusion resulting from overuse of symbolic links, and the athethic preferences of different people. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Statically linked binaries Linux is currently running on a wide variety of systems, some single user with small disks, some as servers in large networked environments. Because of this variety, this standard sets no rule regarding what binaries are static or dynamic with the following two exceptions. Both 'ln' and 'sync' should have static versions in /sbin in addition to dynamic versions in /bin since everyday users may wish to run these too. Large Linux systems may wish to include other statically linked binaries (sh, init, mkfs, fsck, tunefs, mount, umount, swapon, swapoff, getty, login, etc.). The developers and/or system administrators are free to statically/dynamically link these and other binaries as they see fit, as long as the location of the binaries doesn't change. Networked systems (especially those of the future which may lack floppy drives), may want to make ifconfig, route, hostname, and ftp (meaning an additional static copy in /sbin) static as well. ------------------------------------------------------------------------ ACKNOWLEDGEMENTS Credit for this text should be given to the FSSTND activists, developers, users, and system administrators whose input was essential to this standard. I also wish to thank each of the contributors who helped me to write, compile, and compose this, a consensus standard. ------------------------------------------------------------------------ Contributors: [in alphabetical order] Drew Eckhardt Ian Jackson Ian McCloghrie Daniel Quinlan Mike Sangrey David H. Silber Theodore Ts'o Stephen Tweedie