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AIXPerl

Added by OneSkyWalker, last edited by OneSkyWalker on Feb 17, 2011 (view change)

Hints and tips when using Perl

On some recent technology levels of AIX V5.3 and V6.1, Perl can fail unexpectedly with "Out of memory!" or

"Segmentation fault(coredump)" error messages. That's because Perl on those technology levels was compiled

without the -b maxdata:0x80000000 option. To confirm that the problem is indeed the maxdata option, set the

LDR_CNTRL environment variable to override the maxdata setting:

export LDR_CNTRL=MAXDATA=0x80000000

and run the failing Perl script again to confirm that it does not fail. If the Perl script still fails, the maxdata setting

is not causing the failure and the issue is likely with ulimits or a shortage of paging space.

Please note that the LDR_CNTRL setting above can cause issues for other executables, so running with

LDR_CNTRL set by default is not a good idea.

The AIX ldedit command can be used to patch the Perl executable to change the maxdata setting with which it

is run.

isdtest1# which perl

/usr/bin/perl

isdtest1# ls -altr /usr/bin/perl

lrwxrwxrwx 1 root system 28 Feb 04 21:21 /usr/bin/perl ->

/usr/opt/perl5/bin/perl5.8.8

isdtest1# cd /usr/opt/perl5/bin

isdtest1# ls -altr perl*

-rwxr-xr-x 1 root system 11967 Jun 03 2009 perlivp

-rwxr-xr-x 1 root system 244 Jun 03 2009 perldoc

-rwxr-xr-x 1 root system 17973 Jun 03 2009 perlcc

-rwxr-xr-x 1 root system 37295 Jun 03 2009 perlbug

-rwxr-xr-x 2 root system 147543 Jun 03 2009 perl5.8.8

-rwxr-xr-x 2 root system 147543 Jun 03 2009 perl

-rwxr-xr-x 1 root system 11967 Jun 03 2009 perlivp_64bit

-rwxr-xr-x 1 root system 37295 Jun 03 2009 perlbug_64bit

-rwxr-xr-x 2 root system 149946 Jun 03 2009 perl_64bit

-rwxr-xr-x 2 root system 149946 Jun 03 2009 perl5.8.8_64bit

-rwxr-xr-x 1 root system 17973 Jun 30 2009 perlcc_64bit

-rwxr-xr-x 1 root system 244 Jun 30 2009 perldoc_64bit

isdtest1# df -k .

Filesystem 1024-blocks Free %Used Iused %Iused Mounted on

/dev/hd2 2359296 644104 73% 40213 21% /usr

isdtest1# cp -ip perl5.8.8 perl5.8.8.patched

isdtest1# dump -ov perl5.8.8.patched

perl5.8.8.patched:

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***Object Module Header***

# Sections Symbol Ptr # Symbols Opt Hdr Len Flags

{{ 5 0x00010eec 3022 72 0x1002}}

Flags=( EXEC DYNLOAD DEP_SYSTEM )

Timestamp = "Jun 02 03:13:37 2009"

Magic = 0x1df (32-bit XCOFF)

***Optional Header***

Tsize Dsize Bsize Tstart Dstart

0x00001da8 0x00000630 0x00000008 0x10000150 0x20000ef8

SNloader SNentry SNtext SNtoc SNdata

0x0004 0x0002 0x0001 0x0002 0x0002

TXTalign DATAalign TOC vstamp entry

0x0007 0x0003 0x200013fc 0x0001 0x2000137c

maxSTACK maxDATA SNbss magic modtype

0x00000000 0x00000000 0x0003 0x010b 1L

isdtest1# ldedit -b maxdata:0x80000000 perl5.8.8.patched

ldedit: File perl5.8.8.patched updated.

isdtest1# dump -ov perl5.8.8.patched

perl5.8.8.patched:

***Object Module Header***

# Sections Symbol Ptr # Symbols Opt Hdr Len Flags

5 0x00010eec 3022 72 0x1002

Flags=( EXEC DYNLOAD DEP_SYSTEM )

Timestamp = "Jun 02 03:13:37 2009"

Magic = 0x1df (32-bit XCOFF)

***Optional Header***

Tsize Dsize Bsize Tstart Dstart

0x00001da8 0x00000630 0x00000008 0x10000150 0x20000ef8

SNloader SNentry SNtext SNtoc SNdata

0x0004 0x0002 0x0001 0x0002 0x0002

TXTalign DATAalign TOC vstamp entry

0x0007 0x0003 0x200013fc 0x0001 0x2000137c

maxSTACK maxDATA SNbss magic modtype

0x00000000 0x80000000 0x0003 0x010b 1L

isdtest1# cd /usr/bin

isdtest1# ls -altr perl

lrwxrwxrwx 1 root system 36 Feb 04 21:21 perl ->

/usr/opt/perl5/bin/perl5.8.8

isdtest1# ln -sf /usr/opt/perl5/bin/perl5.8.8.patched perl

isdtest1# ls -altr perl

lrwxrwxrwx 1 root system 36 Feb 07 17:33 perl ->

/usr/opt/perl5/bin/perl5.8.8.patched

isdtest1#

When a 32-bit executable is compiled without maxdata, the executable's stack and data is restricted to a single

256 MB segment. Setting maxdata to 0x80000000 lifts the 256 MB restriction to 0x80000000 = 2147483648 bytes

= 2 GB, or eight 256 MB segments.

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5

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= 2 GB, or eight 256 MB segments.

BTW, the Getting more memory in AIX for your Java applications article has a good explanation of how maxdata

works and what it does. In the article, see Figure 1 and the text which precedes and follows it.

Another option is to run the 64-bit version of Perl, but please note that the same Perl script will consume

more virtual and real memory when run with the 64-bit version of Perl. To use the 64-bit version of Perl, change

the hash-bang line (the first in the shell script) to point to the 64-bit executable. For example:

#!/usr/opt/perl5/bin/perl5.8.8_64bit

My thanks to Chris Shortes (Jay C Shortes/Dallas/IBM) for pointing out that the maxdata setting overrides soft

ulimits and that AIX does not enforce the memory ulimit.

So, when running versions of Perl compiled without maxdata (the 64-bit version is typically compiled

without maxdata), it is often necessary to alter the default data ulimit:

isdtest1# ulimit -a

time(seconds) unlimited

file(blocks) 2097151

data(kbytes) 131072

stack(kbytes) 32768

memory(kbytes) 32768

coredump(blocks) 2097151

nofiles(descriptors) 2000

threads(per process) unlimited

processes(per user) unlimited

isdtest1#

In the example above, the data ulimit will restrict Perl compiled without maxdata to 131072/1024 = 128 MBs.

First, check the hard ulimits:

isdtest1# ulimit -Ha

time(seconds) unlimited

file(blocks) 2097151

data(kbytes) unlimited

stack(kbytes) 4194304

memory(kbytes) unlimited

coredump(blocks) unlimited

nofiles(descriptors) unlimited

threads(per process) unlimited

processes(per user) unlimited

isdtest1#

Then, increase the soft data ulimit:

isdtest1# ulimit -Sd 2097152

isdtest1# ulimit -a

time(seconds) unlimited

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time(seconds) unlimited

file(blocks) 2097151

data(kbytes) 2097152

stack(kbytes) 32768

memory(kbytes) 32768

coredump(blocks) 2097151

nofiles(descriptors) 2000

threads(per process) unlimited

processes(per user) unlimited

isdtest1#

Be careful

Don't use ulimit -d 2097152, which will change the hard data ulimit. When the hard

data ulimit is changed on a userid other than root, it can only be changed to a value

lower than the current hard data ulimit. Always specify the -S flag to set the soft

ulimit. If a hard ulimit is inadvertently reduced to a value which is too low, log off and

log back on again. The new shell will revert to the default hard ulimits.

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