Wednesday October 04, 2006

Changing Search Paths with crle(1) - they are a replacement

A developer who wished to add /usr/sfw/lib to their default runtime search path, managed to turn their system into a brick by using crle(1):

    # crle -l /usr/sfw/lib
    # ls
    ld.so.1: ls: fatal: libsec.so.1: open failed: No such file or directory
    Killed

The problem was that crle(1),in this basic form, created a system wide configuration file. This configuration file defined that the default runtime search path for shared object dependencies is /usr/sfw/lib. This search path definition had replaced the standard defaults.

You can determine the standard search path defaults using crle(1).For example, without any system wide configuration file, the following defaults might exist:

   $ crle

   Default configuration file (/var/ld/ld.config) not found
     Platform:     32-bit LSB 80386
     Default Library Path (ELF):   /lib:/usr/lib  (system default)
     Trusted Directories (ELF):    /lib/secure:/usr/lib/secure  (system default)

This user had effectively removed the system default search paths, and hence the runtime linker, ld.so.1,had been unable to find the basic dependencies required by all applications. The new configuration file revealed:

   $ crle

   Configuration file [version 4]: /var/ld/ld.config
     Platform:     32-bit LSB 80386
     Default Library Path (ELF):   /usr/sfw/lib
     Trusted Directories (ELF):    /lib/secure:/usr/lib/secure  (system default)

   Command line:
     crle -c /var/ld/ld.config -l /usr/sfw/lib

The -l option allows you to define new search paths. However, rather than dictate that a new search path definition be prepended, inserted, or appended to any existing search paths, crle(1) simply replaces any existing search paths. The man page spells this out in some detail:

    -l dir
      ....
      Use of this option replaces  the  default  search  path.
      Therefore,  a  -l option is normally required to specify
      the original system default in relation to any new paths
      that are being applied. ....

Therefore, to prepend the new search path to the existing defaults you should specify each search path:

    # crle -l /usr/sfw/lib -l /lib -l /usr/lib
    # ls
    devices/        lib/            proc/
    ....

An alternative is to use the -u, update, option. Any new search paths supplied with crle(1) are appended to any existing search paths. Even if an existing configuration file does not exist, the -u option causes any new search paths to be appended to the system defaults:

   # crle -u -l /usr/sfw/lib
   # crle

   Configuration file [version 4]: /var/ld/ld.config
     Platform:     32-bit LSB 80386
     Default Library Path (ELF):   /lib:/usr/lib:/usr/sfw/lib
     Trusted Directories (ELF):    /lib/secure:/usr/lib/secure  (system default)

   Command line:
     crle -c /var/ld/ld.config -l /lib:/usr/lib:/usr/sfw/lib

Note that the usage message from crle(1) is a little misleading, as it implies that the new search path is an addition:

   # crle -X
   crle: illegal option -- X
       ....
       [-l dir]        add default search directory
       ....

We'll get the usage message updated to be more precise.

Remember, should you ever get in trouble with crle(1) configuration files, you can always instruct the runtime linker to ignore processing the configuration file by setting the environment variable LD_NOCONFIG=yes:

   # crle -l /does/not/exist
   # ls
   ld.so.1: ls: fatal: libsec.so.1: open failed: No such file or directory
   Killed
   # LD_NOCONFIG=yes ls
   devices/        lib/            proc/
   ....
   # LD_NOCONFIG=yes rm /var/ld/ld.config
   # ls
   devices/        lib/            proc/
   ....

It is recommended that when creating a new configuration file, you first create the file in a temporary location. The environment variable LD_CONFIG can then be set to this new configuration file. Refer to the crle(1) man page for an example.

Note. crle(1) should not be crippled by blowing away the system default search paths:

   # crle -l /does/not/exist
   # crle

   Configuration file [version 4]: /var/ld/ld.config
     Platform:     32-bit MSB SPARC
     Default Library Path (ELF):   /does/not/exist
     Trusted Directories (ELF):    /lib/secure:/usr/lib/secure  (system default)

   Command line:
     crle -c /var/ld/ld.config -l /does/not/exist

   # elfdump -d /usr/bin/crle | fgrep RPATH
   ld.so.1: fgrep: fatal: libc.so.1: open failed: No such file or directory
   ksh: 18184 Killed
   # LD_NOCONFIG=yes; export LD_NOCONFIG
   # elfdump -d /usr/bin/crle | fgrep RPATH
      [6]  RPATH             0x61b               $ORIGIN/../lib

Using $ORIGIN within a runpath provides crle(1) with a level of protection against insufficient configuration file information.

(2006-10-04 14:48:41.0) Permalink Comments [1]