HP-UX Reference (11i v1 05/09) - 5 Miscellaneous Topics (vol 9)

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dld.sl(5) dld.sl(5)

The potential problems are :

• If the library has initializers/terminators, they will be called twice

• you may end up using two different copies of the same data symbol which may cause incorrect

behavior

You can specify multiple libraries as part of the

LD_PRELOAD environment variable. Separate the

libraries by spaces or colons as in

LD_LIBRARY_PATH. (Multi-byte support is not provided as part of

parsing the

LD_PRELOAD library list). You can specify

LD_PRELOAD libraries with absolute paths or

relative paths. The

LD_PRELOAD libraries can also consist of just the library names, in which case the

dynamic loader uses the directory path list in the environment variables

LD_LIBRARY_PATH

and/or

SHLIB_PATH or the embedded path list (if enabled) to search for the libraries.

The dynamic loader does not issue an error or warning message if it cannot ﬁnd a library speciﬁed by

LD_PRELOAD . However, if it does not ﬁnd a dependent of the

LD_PRELOAD libraries, the dynamic

loader issues the same error message as if the

LD_PRELOAD library is speciﬁed in the link line.

The LD_PRELOAD_ONCE Environment Variable

The

LD_PRELOAD_ONCE feature is similar to

LD_PRELOAD except that the dynamic loader, dld.sl,

unsets

LD_PRELOAD_ONCE after reading it, so that any applications invoked by the current application

do not have

LD_PRELOAD_ONCE

set. This is useful in situations where the current application needs cer-

tain libraries preloaded while the child application is adversely affected if these are preloaded (for example,

ksh terminates abnormally if LD_PRELOAD contains /usr/lib/libpthread.1

). The libraries

speciﬁed by

LD_PRELOAD_ONCE

are loaded before the ones speciﬁed by LD_PRELOAD . The effect on

symbol resolution is that the symbols from libraries speciﬁed by

LD_PRELOAD_ONCE

take precedence

over symbols from libraries speciﬁed by

LD_PRELOAD .

Running Setuid Programs

For looking up shared libraries for setuid applications, the dynamic loader uses only the paths listed in

/etc/dld.sl.conf.

LD_LIBRARY_PATH

and SHLIB_PATH are set, they are validated against the list of paths in

/etc/dld.sl.conf

. (This allows the individual applications to appropriately order the list from the

conf ﬁle).

You can turn this feature off by setting the option _HP_DLDOPTS to -no_setuidpath

. Using this

option disables setuid programs from all dynamic path lookup.

The conﬁguration ﬁle

/etc/dld.sl.conf

is expected to contain a list of shared library search paths

(delimited by either colon or newline characters). To avoid redundant searches, you should see that one

path appears only once in the ﬁle (and also in the options

SHLIB_PATH and LD_LIBRARY_PATH

). The

conf ﬁle should be writeable only by root. Otherwise, the loader does not use its contents. If

/etc/dld/sl.conf does not exist or has the wrong permissions, all dynamic path lookup is disabled.

Any relative paths (paths not starting with slash (

/) in the path list are ignored by the loader.

NOTE: Spaces are not allowed in the paths listed. Everything on a line that follows a space or

# character

is ignored. You can use

# to comment out paths in the ﬁle.

If either SHLIB_PATH or LD_LIBRARY_PATH

is set, and neither contains any path listed in the conf

ﬁle, all dynamic path lookup is disabled. The paths from the config ﬁle are not a fallback.

The following is a sample conﬁguration ﬁle:

# need this for some GNU and shared apps

/usr/local/lib:/nfs/appserver/lib

# path below is ignored: path not starting with ’/’

# and loader will not expand ˜ etc.

~wizkid/lib

# second path below ignored: space

/user/ipfguru/lib/hpux32: user/ipfguru/lib/hpux64

/net/appserv2/local/lib # ignored:line starting with space

/opt/java1.3/jre/lib/PA_RISC2.0/ # java 1.3 PA32

Section 5−−46 Hewlett-Packard Company − 6 − HP-UX 11i Version 1: September 2005