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C    Enabling and Disabling Extended UID/GID Support

With DIGITAL UNIX Version 4.0D, you can enable or disable extended UID and GID support, as described in Section 1.2, by following the instructions in this appendix.

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C.1    Enabling Extended UID and GID Support

To enable extended UID and GID support, do the following:

  1. Become the root user.

  2. Use the sysconfigdb utility to add the following attribute to the proc subsystem of the /etc/sysconfigtab file: 

    enable_extended_uids=1

    Alternatively, you can use the dxkerneltuner graphical user interface to set this attribute.

  3. Reboot the system.

Extended UID and GID support is now enabled.

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C.2    Disabling Extended UID and GID Support

To disable extended UID and GID support, do the following:

  1. Become the root user.

  2. Use sysconfigdb or dxkerneltuner to set the enable_extended_uids attribute to 0 in the /etc/sysconfigtab file: 

    enable_extended_uids=0

  3. Reboot the system.

Extended UID and GID support is now disabled.

Note

When extended UIDs and GIDs are disabled, files owned by a user with an extended UID or GID will be inaccessible to all users except root. Any user with an extended UID or GID will not have access to log in to the system or use the su command to access their accounts.

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C.3    Checking for Extended UID and GID Support

The following sample program demonstrates how to check the maximum number of UIDs supported by a version of the DIGITAL UNIX operating system. The maximum number of GIDs will always be the same as the maximum number of UIDs: 


 

#include <unistd.h>
#include <limits.h>
#include <errno.h>

 

#include <sys/table.h>

 

#ifndef TBL_UIDINFO
#define TBL_UIDINFO 56
#endif

 

main()
{
     uid_t uid_max;

 

     errno = 0;

 

     uid_max = table (TBL_UIDINFO, 0, (char *)0, 1, 0);

 

     if ((errno != 0) && ((int)uid_max < 0))
          uid_max = UID_MAX;

 

     printf(%d\n", uid_max);

 

}

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C.4    Applications Affected by Extended UIDs and GIDs

The following programs are affected by extended UID and GID support.

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C.4.1    Clusters

Extended UID and GID support can be enabled in a TruCluster Available Server Software or TruCluster Production Server Software configuration only after all member systems have installed (or upgraded to) Version 1.5 of the appropriate TruCluster software product. To enable extended UID or GID support, set the enable_extended_uids parameter on every system as directed in this appendix and reboot every system. Do not use extended UIDs and GIDs on any member system until you have rebooted the last member system.

Once you have enabled extended UID and GID support in a cluster, you must not disable it. Disabling this support will disrupt the operation of your cluster.

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C.4.2    Kerberos

Kerberos Version 4 does not support extended UIDs and GIDs. If you use Kerberos Version 4 and need extended UID and GID support, you should upgrade to Kerberos Version 5.

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C.4.3    System V File System

The System V File System (S5FS) does not support extended UIDs and GIDs. File system syscalls that specify UIDs and GIDs greater than 65,535 will return an EINVAL error. Users assigned a UID or GID greater than 65,535 will not be able to create or own files on a System V File System. Consider using the UFS, MFS, or AdvFS for a workaround.

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C.4.4    The ls Command

The ls -l command does not display the disk block usage on quota files or sparse files. This is not a result of the implementation of extended UIDs and GIDs, but rather a result of the behavior of the ls -l command. When extended UIDs and GIDs are enabled, quota files and sparse files may appear much larger than expected. To display the actual disk block usage for any file, use the ls -s command.

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C.4.5    The cp Command

The cp command will incorrectly copy quota files or other sparse files. This is not a result of the implementation of extended UIDs and GIDs, but rather a result of the behavior of the cp command when it reads a file. When extended UIDs and GIDs are enabled, quota files and other sparse files may be copied to a new file that is much larger than expected. To correctly copy quota files or other sparse files, use the dd command with the conv=sparse parameter.

%  dd conv=sparse if= inputfile  of= outputfile

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C.4.6    The vdump/vrestore Utilities and UFS File Systems

If a UFS file system that contains quota files or other sparse files is backed up using the vdump utility and restored using the vrestore utility, the quota files or other sparse files will be restored as follows:

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C.4.7    The dxarchiver Utility

The dxarchiver utility does not support extended UIDs and GIDs. However, the pax and tar utilities do support extended UIDs and GIDs and can be used as alternatives. If you need to use the dxarchiver utility, you must not enable extended UID or GID support.

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C.4.8    The cpio Utility

The cpio utility does not support extended UIDs and GIDs. However, the pax and tar utilities do support extended UID and GIDs and can be used as alternatives. If you need to use the cpio utility, you must not enable extended UID or GID support.

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C.4.9    The pax Utility

The pax utility, used to extract, list, or write archive files has been modified to support long file names and extended UID/GID values

To take advantage of these enhancements, specify the xtar format with the -x option. The following text has been added to the description of the -x option on the pax reference page: 

xtar  Extended tar interchange format.  The default blocking value
      for his format for character special archive files is 10240.
      Blocking values from 512 to 32,256 in increments of 512
      are supported.  This option lets the user archive long file
      names and extended UID/GID values.

On the reference page, the xtar format may be incorrectly identified as the ustar format. The correct syntax is -x xtar.

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C.4.10    The tar Utility

The tar utility, used to extract, list, or write archive files has been modified to support long file names and extended UID/GID values

To take advantage of these enhancements, specify the -E option when using the tar utility.

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C.4.11    PATHWORKS

PATHWORKS does not support extended UIDs and GIDs. If you use PATHWORKS and need extended UID or GID support, you should upgrade to Version 4.0 or higher of Advanced Server for DIGITAL UNIX (ASDU).