This section provides information necessary to run ClearCase on Linux platforms, with references to other places in the documentation set where more information can be obtained. Installation-related information can be found in the Installation Guide.
A root user of ClearCase will find that the Linux operating system’s NFS implementation can cause some unexpected behavior. For example, using the default /etc/exports file, root can create a view that cannot be removed by root.
If, when using Linux NFS and the automounter, a user references /net/hostname, the host is NFS mounted on the mount point specified in the automounter configuration file. This is true even if the user is currently on host. The default rule for NFS mounts—unless explicitly overridden in the /etc/exports file—is to map requests from uid/gid=0 (that is, root) to the anonymous uid/gid. This means that under the default configuration, a file owned by root cannot be removed by root by means of the /net/hostname path.
ClearCase creates files locally, but accesses these files through global path specifications (by default, /net/hostname/...). Therefore, if root creates a view on the local machine, all the special files that ClearCase creates in the view are owned by root. However, if root tries to remove the view, the view is accessed through the global path, and the special ClearCase files are not deleted because the ownership and permissions do not allow deletion by the anonymous user.
Workaround: To avoid this problem, the /etc/exports entries must include the option no_root_squash. This option allows all ClearCase activities to proceed normally. Note that you must exercise caution when using the no_root_squash option because it allows any root user—on any host that NFS mounts a host’s exported file system—to have root permissions on that file system. This can be a dangerous security problem in some environments.
Typically, root does not create views, and the problem arises only on those ClearCase administrative tasks that require root privileges, for example, using the protectvob command. In such cases, it is recommended that the modifications to /etc/exports be temporary and that the original settings be restored after the ClearCase administrative tasks are performed.
Note: The use of /net/hostname in global paths is pervasive in ClearCase: the inability of ClearCase to access files through these global paths can cause anomalous behavior, often with no warning. Correct configuration of Linux to allow proper ClearCase access is essential for successful ClearCase operation.
If you use Linux as a VOB server, you may receive intermittent error messages in ClearCase because of NFS caching issues in the Linux operating system. In most cases, when you perform the same ClearCase operation again, it succeeds.
The ClearCase configurations listed below are less likely to experience these problems:
The Linux mount command does not properly mount file systems other than those included in the default distribution. If you try to mount a ClearCase MVFS with the Linux mount command, you will cause a kernel fault and must reboot your system.
Workaround: Always use the cleartool mount command to mount VOBs.
Because of limitations in the interfaces between NFS and the MVFS, non-ClearCase access using NFS is not supported. Exporting MVFS file systems is unsupported on Linux systems.
The slocate(1) command on Linux provides a form of indexed find. Just as you should avoid having the find command descend into the viewroot at /view, you should also prevent slocate from doing so. You can accomplish this by issuing the slocate command with the -f command line option and the mvfs file type.
If the slocate command is in /etc/cron.daily/slocate.cron, this change is made for you during installation and appears in the install log.
Because of limitations in the interface between the MVFS and Linux, when set to a view, it is not possible to perform certain file operations—such as the mv command—on sockets, character devices, and block devices. For example, if you attempt to rename the character device ptyx3 using the command
# mv ptyx3 foo
the following error message appears:
mv: cannot move ‘ptyx3’ to subdirectory of itself ‘foo’
Workaround: Perform these file operations outside a view context.
The Linux kernel and the vnode module must be built using the same compiler and the same kernel heading. See the file, /var/adm/rational/clearcase/mvfs/vnode_src/README.txt, for details.
This section discusses general issues related to Rational ClearCase 2002.05.00 and later on IBM mainframes running Linux.
The following are known limitations:
Moved to the install guide (6.0NR?)