Beyond the limits - environment

1. Prerequisites
My environmnet is based on Solaris 10  10 9/10  with 640 MB of memory and CentOS 5.5 2.6.18-194.26.1.el5 with 512 MB, standard installation both of them run in VMWare environmnet. For shell I use bash (as common)

bash-3.00# bash --version
GNU bash, version 3.00.16(1)-release (i386-pc-solaris2.10)
Copyright (C) 2004 Free Software Foundation, Inc.


[root@centos ~]# bash --version
GNU bash, version 3.2.25(1)-release (i686-redhat-linux-gnu)
Copyright (C) 2005 Free Software Foundation, Inc.

All the tests will be done with default settings of the OS and environment

2. Test the maximum length variable
the script i will use is sample:

TEMPVAR=A
for i in {1..10000};
        do
        TEMPVAR=${TEMPVAR}$TEMPVAR;
        a=$(echo 2^$i+1|bc)
        b=$(echo $TEMPVAR|wc -c)
        if [ $a -ne $b ]
        then echo KO - $a, $b
        else echo $a
        fi
done
 2.1. And the execution in Linux


[root@centos ~]# ./z1.sh
3
5
<snip>
67108865
134217729
./z1.sh: xmalloc: cannot allocate 268435457 bytes (0 bytes allocated)
KO - 268435457, 0
[1]+  Stopped                 ./z1.sh
[root@centos ~]# vmstat 1 2
procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 0  0  10716 229500  25160 228524   66  139   138   178 1011  151 18 18 61  3  0
 0  0  10716 229500  25160 228524    0    0     0     0 1013   15  0  0 100  0  0
 As you can see above I get error allocating memory beyond the size of free memory
2.2. Execution in Solaris

bash-3.00# ./z1.sh
3
5
<snip>
8388609
16777217
./z1.sh: fork: Not enough space
./z1.sh: line 7: [: 33554433: unary operator expected
33554433
./z1.sh: fork: Not enough space
bash-3.00# vmstat 1 2
 kthr      memory            page            disk          faults      cpu
 r b w   swap  free  re  mf pi po fr de sr cd f0 s0 --   in   sy   cs us sy id
 0 0 0 856808 174100 50 1101 0  1  5  0 66  2 -0  3  0  336  801  308  9  7 84
 0 0 0 749832 70472   3  43  0  0  0  0  0 27  0  0  0  326  300  185  1  9 90
 
 The similar is situation in Solaris where i can allocate even less that half of free memory
Of course it is not very wise to use such variables, but who knows?
3. Number of commandline arguments
3.1. Sample C program
Next I will try to check what is the maximum of commandline arguments of one sample C program

#include <stdio.h>
int main(int argc, char *argv[])
{
        printf("%d\n", argc);
}

and the shell script I will use is

TEMPVAR=A
for i in {1..1000}
do
TEMPVAR="$TEMPVAR $TEMPVAR"
a=$(./a.out $TEMPVAR)
echo $a
done
 

3.1.1 On Linux

[root@centos ~]# cc z2.c
[root@centos ~]# ./a.out 1
2
[root@centos ~]# ./a.out 1 2
3
[root@centos ~]# ./z2.sh
3
5
<snip>
524289
1048577
./z2.sh: line 5: ./a.out: Argument list too long

 1m of arguments, that pretty much :)
3.1.2 Solaris

bash-3.00# /usr/sfw/bin/gcc z2.c
bash-3.00# ./a.out 1
2
bash-3.00# ./a.out 1 2
3
bash-3.00# ./z2.sh
3
5
<snip>
65537
131073
./z2.sh: line 5: ./a.out: Arg list too long
"Just" 128k, not so much as Linux, but anyway do someone will use so many for practical puspose?


3.2. Sample shell program
Next I will try to check what is the maximum of commandline arguments of one very sample shell program

echo $#

 using this shell script

TEMPVAR=A
for i in {1..1000}
do
TEMPVAR="$TEMPVAR $TEMPVAR"
a=$(./z2test.sh $TEMPVAR)
echo $a
done
 
 This time the results appear mich slower because of the invocation of subshell.
3.2.1 Linux
After 1 hour of waiting I stop the script, but before this I see in top

29827 root      25   0 47028  41m  476 R 99.9  8.3   2:38.86 bash

3.2.2. Solaris
The same (long waiting) happen in Solaris and after 128k i see in prstat

 15100 root       72M   69M run     20    0   0:09:01  96% bash/1

As conclusion 128K is the maximum practicle limit of number command line arguments