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Set LD_LIBRARY_PATH to 1 or empty

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Operating Systems AIX Set LD_LIBRARY_PATH to 1 or empty
# 1  
Old 12-11-2012
Set LD_LIBRARY_PATH to 1 or empty
I have a question on setting environmental variable LD_LIBRARY_PATH.
The case is that, i cannot execute wget on my AIX machine.
It return the following error:
Code:
exec(): 0509-036 Cannot load program wget because of the following errors:
        0509-022 Cannot load module /opt/freeware/lib/libintl.a(libintl.so.8).
        0509-150   Dependent module /usr/lib/libiconv.a(libiconv.so.2) could not be loaded.
        0509-152   Member libiconv.so.2 is not found in archive
        0509-022 Cannot load module wget.
        0509-150   Dependent module /opt/freeware/lib/libintl.a(libintl.so.8) could not be loaded.
        0509-022 Cannot load module .

After I unset the environmental variable LD_LIBRARY_PATH using "unset" command, wget can working properly.
Then I set the variable to "1", wget also working properly.
Finally, I set it to "", wget prompt the above error message again.
So, would you tell me what going on? and why wget can working even $LD_LIBRARY_PATH="1"?

thank you very much
# 2  
Old 12-11-2012
First off,

Code:
$LD_LIBRARY_PATH="1"

Will not set the variable "LD_LIBRARY_PATH", but a variable of the name whatever "$LD_LIBRARY_PATH" will evaluate to. Maybe it was only a typo of yours, i mention this just to be sure.

Second, "LD_LIBRARY_PATH" works like the "PATH" variable, just for libraries instead of executables. Why it works if you set it to the nonsense value of "1" i don't know. Whenever you create a new shell, "/etc/environment" and your local user environment (most times "~/.kshrc") is read and parsed in, probably presetting "LD_LIBRARY_PATH" to some sensible value. Have a look there to which value it is set.

I hope this helps.

bakunin
# 3  
Old 12-11-2012
What is LD_LIBRARY_PATH before you change it?
# 4  
Old 12-11-2012
Firstly, I set LD_LIBRARY_PATH in my .profile as following:

export LD_LIBRARY_PATH=""

Then wget does not work.
After that, I change LD_LIBRARY_PATH as mention.
What I want to know is how the system behave when the LD_LIBRARY_PATH set to empty or null?So, that wget does not work.
# 5  
Old 12-12-2012
Quote:
Originally Posted by cstsang
What I want to know is how the system behave when the LD_LIBRARY_PATH set to empty or null?So, that wget does not work.
OK, let us start from the beginning: there has to be some way the system knows where to load shared libraries, analogous to the way it has to know where to load executables. For executables, there is the "PATH" variable and for (shared) libraries there is the variable "LD_LIBRARY_PATH". This is so in every Unix derivate.

AIX now usually ignores the value of "LD_LIBRARY_PATH" (unlike, for instance, Solaris) and uses the value of "LIBPATH" instead for the same purpose. So if a program written for "generic Unix" tells you to set LD_LIBRARY_PATH to some value you can safely change this for "LIBPATH" if you are using AIX.

BUT - and now it comes: every program has to be compiled and linked before it can be run. In AIX, if LIBPATH is set when the linker ("ld") is invoked, then the resulting executable will ignore the setting of "LIBPATH" and use the value set at link time instead. One can override this behavior by using the "-L" flag for "ld".

If you want to know with which flags/settings a program is linked with use the "dump -n" command against the binary.

I hope this helps.

bakunin
# 6  
Old 12-12-2012
dump -H
Code:
dump -H

lists information about expected library paths and names.

I do not have wget installed, so I cannot provide that example - here is another one:

Code:
michael@x054:[/home/michael]dump -H /opt/httpd/sbin/httpd

/opt/httpd/sbin/httpd:

                        ***Loader Section***
                      Loader Header Information
VERSION#         #SYMtableENT     #RELOCent        LENidSTR
0x00000001       0x000003ec       0x00000c11       0x00000091       

#IMPfilID        OFFidSTR         LENstrTBL        OFFstrTBL
0x00000007       0x0000ef0c       0x00005002       0x0000ef9d       


                        ***Import File Strings***
INDEX  PATH                          BASE                MEMBER              
0      /opt/lib:/usr/vac/lib:/usr/lib:/lib                                         
1                                    libpcre.a           libpcre.so.1        
2                                    libaprutil.so                           
3                                    libapr.so                               
4                                    libpthread.a        shr_xpg5.o          
5                                    libc.a              shr.o               
6                                    librtl.a            shr.o

The INDEX 0 is the default library search path the binary will use. If you set a LD_LIBRARY_PATH you override that, and maybe your libraries are not searching properly.

Also note: TE (trusted execution) can prevent you from using LD_LIBRARY_PATH - to prevent someone from being able to insert a trojan library.

Hope this helps!
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