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diff --git a/sbin/mount_umap/umap_manual b/sbin/mount_umap/umap_manual deleted file mode 100644 index 50a8ce5..0000000 --- a/sbin/mount_umap/umap_manual +++ /dev/null @@ -1,175 +0,0 @@ - -\appendix -\section{The umap Layer} \label{sect:umap} - -\subsection{Introduction} - -Normally, the file system is expected to span a single administrative domain. -An administrative domain, for these purposes, is a machine or set of -machines that share common password file information, usually through -the yellow pages mechanism. File hierarchies that span more -than one domain leads to certain problems, since the same numerical -UID in one domain may correspond to a different user in another domain. -If the system administrator is very careful to ensure that both domains -contain identical user ID information, the umap layer can be used to -run between those domains without changes - -The umap layer is a file system layer that sits on top of the normal -file layer. The umap layer maps Unix-style UIDs from -one domain into the UIDs in the other domain. By setting up the mappings -properly, the same user with different UIDs in two domains can be seen -as the same user, from the system point of view, or, conversely, two -different users with the same UID in the two domains can be distinguished. - -First, we define some terms. ``User'' refers to the human (or daemon) that -has privileges to login, run programs, and access files. ``UID''refers to -the numerical identifier that uniquely identifies the user within a -single domain. ``Login name'' refers to the character string the user -types to log into the system. ``GID'' refers to the numerical group -identifier used by Unix systems to identify groups of users. ``Group -name'' is the character string name attached to a particular GID in the -local {\sf /etc/groups} file or the yellow pages groups file. - -In order for the umap layer to work properly, all users -in either domain must have password file entries in both domains. -They do not, however, have to have the same numerical UID, nor even the -same character string login name (the latter is highly recommended, -if possible, however). Any user not having a UID in one domain will be -treated as the special user NOBODY by the other domain, probably with -undesirable consequences. Any user not owning any files in the shared -sub-trees need not be given a UID in the other domain. - -Groups work similarly. The umap layer can translate group ID's between -domains in the same manner as UID's. Again, any group that wishes to -participate must have a group ID in both domains, -though it need not be the same GID in both. If a group in one domain is not -known in the other domain, that group will be treated as being NULLGROUP. -The umap layer has no provisions for enrolling UID's from other domains -as group members, but, since each user from each domain must have some -UID in every domain, the UID in the local domain can be used to enroll -the user in the local groups. - -NOBODY and NULLGROUP are special reserved UID's and GID's, respectively. -NOBODY is user 32767. NULLGROUP is group 65534. If the system administrator -wants to have an appropriate text string appear when these UID's are -encountered by programs like {\sf ls -l}, he should add these values to -the password and {\sf /etc/groups} file, or to the appropriate yellow pages. -If these IDs are already in use in that domain, different values can be -used for NOBODY and NULLGROUP, but that will require a recompilation of -the umap layer code and, as a result, the entire kernel. These -values are defined in the {\sf umap\_info.h} file, kept with the rest of the -umap source code. - -When the umap layer is in use, one of the participating domains is declared -to be the master. All UID and GID information stored for participating files -will be stored in vnodes using its mappings, no matter what site the copies of -the files are stored at. The master domain therefore need not run a copy -of the umap layer, as it already has all of the correct mappings. All -other domains must run a umap layer on top of any other layers they use. - -\subsection{Setting Up a umap Layer} - -The system administrator of a system needing to use the umap layer -must take several actions. -First, he must create files containing the necessary UID -and GID mappings. There is a separate file for user and group IDs. The -format of the files is the same. The first line contains the total number -of entries in the file. Each subsequent line contains one mapping. A -mapping line consists of two numerical UIDs, separated by white space. -The first is the UID of a user on the local machine. The second is the -UID for the same user on the master machine. The maximum number of users -that can be mapped for a single shared sub-tree is 64. The maximum number of -groups that can be mapped for a single sub-tree is 16. These constants -are set in the {\sf umap\_info.h} file, and can be changed, but changing them -requires recompilation. Separate mapping files can be used for each shared -subtree, or the same mapping files can be shared by several sub-trees. - -Below is a sample UID mapping file. There are four entries. UID 5 is mapped -to 5, 521 to 521, and 7000 to 7000. UID 2002 is mapped to 604. On this -machine, the UID's for users 5, 521, and 7000 are the same as on the master, -but UID 2002 is for a user whose UID on the master machine is 604. All -files in the sub-tree belonging to that user have UID 604 in their inodes, -even on this machine, but the umap layer will ensure that anyone running -under UID 2002 will have all files in this sub-tree owned by 604 treated as if -they were owned by 2002. An {\sf ls -l} on a file owned by 604 in this sub-tree -will show the login name associated with UID 2002 as the owner. - -\noindent4\newline -5 5\newline -521 521\newline -2002 604\newline -7000 7000\newline - -The user and group mapping files should be owned by the root user, and -should be writable only by that user. If they are not owned by root, or -are writable by some other user, the umap mounting command will abort. - -Normally, the sub-tree is grafted directly into the place in -the file hierarchy where the it should appear to users. Using the umap -layer requires that the sub-tree be grafted somewhere else, and -the umap layer be mounted in the desired position in the file hierarchy. -Depending on the situation, the underlying sub-tree can be wherever is -convenient. - -\subsection{Troubleshooting umap Layer Problems} - -The umap layer code was not built with special convenience or -robustness in mind, as it is expected to be superseded with a better -user ID mapping strategy in the near future. As a result, it is not -very forgiving of errors in being set up. Here are some possible -problems, and what to do about them. - -\begin{itemize} - - -\item{Problem: A file belongs to NOBODY, or group NULLGROUP. - -Fixes: The mapping files don't know about this file's real user or group. -Either they are not in the mapping files, or the counts on the number of -entries in the mapping files are too low, so entries at the end (including -these) are being ignored. Add the entries or fix the counts, and either -unmount and remount the sub-tree, or reboot.} - -\item{Problem: A normal operation does not work. - -Fixes: Possibly, some mapping has not been set properly. Check to -see which files are used by the operation and who they appear to be -owned by. If they are owned by NOBODY or some other suspicious user, -there may be a problem in the mapping files. Be sure to check groups, -too. As above, if the counts of mappings in the mapping files are lower -than the actual numbers of pairs, pairs at the end of the file will be -ignored. If any changes are made in the mapping files, you will need to -either unmount and remount or reboot before they will take effect. - -Another possible problem can arise because not all Unix utilities -rely exclusively on numeric UID for identification. For instance, -SCCS saves the login name in files. If a user's login name on two machines -isn't the same, SCCS may veto an operation even though Unix file permissions, -as checked by the umap layer, may say it's OK. There's not much to be -done in such cases, unless the login name can be changed or one fiddles -improperly with SCCS information. There may be other, undiscovered cases -where similar problems arise, some of which may be even harder to handle.} - -\item{Problem: Someone has access permissions he should not have. - -Fixes: This is probably caused by a mistake in the mapping files. Check -both user and group mapping files. If any changes are made in the mapping -files, you will need to unmount and remount the sub-tree or reboot before they -will take effect.} - -\item{Problem: {\sf ls -l} (or a similar program) shows the wrong user for a file. - -Fixes: Probably a mistake in the mapping files. In particular, if -two local UIDs are mapped to a single master UID, stat calls will assign -ownership to the first local UID occurring in the file, which may or may -not be what was intended. (Generally speaking, mapping two local UIDs to -a single master UID is a bad idea, but the software will not prevent it. -Similarly, mapping a single local UID to two master UIDs is a bad idea, -but will not be prevented. In this case, only the first mapping of the -local UID will be done. The second, and all subsequent ones, will be -ignored.) If any changes are made in the mapping files, you will need to -unmount and remount the sub-tree or reboot before they will take effect.} - -\end{itemize} - -\end{document} |
