I found such behaviour of the "getlogin" when maked some asynchronous testsuite with profiling. Simplified examples: 
[dim@grivo out]$ sh -c "/usr/bin/time perl -e '$|=1; print getlogin(),
+ chr(10)'"
dim
0.00user 0.00system 0:00.00elapsed 100%CPU (0avgtext+0avgdata 0maxresi
+dent)k
0inputs+0outputs (0major+393minor)pagefaults 0swaps
[dim@grivo out]$
[dim@grivo out]$
[dim@grivo out]$
[dim@grivo out]$ sh -c "/usr/bin/time perl -e '$|=1; print getlogin(),
+ chr(10)' & wait"

0.00user 0.00system 0:00.00elapsed 50%CPU (0avgtext+0avgdata 0maxresid
+ent)k
0inputs+0outputs (0major+386minor)pagefaults 0swaps
[dim@grivo out]$
[dim@grivo out]$
[dim@grivo out]$
[dim@grivo out]$ sh -c "/usr/bin/time perl -e '$|=1; print \$ENV{USER}
+, chr(10)' & wait"
dim
0.00user 0.00system 0:00.00elapsed 50%CPU (0avgtext+0avgdata 0maxresid
+ent)k
0inputs+0outputs (0major+383minor)pagefaults 0swaps
[dim@grivo out]$
[dim@grivo out]$
[dim@grivo out]$
[dim@grivo out]$ uname -a
Linux grivo.bq 2.6.21-1.3194.fc7 #1 SMP Wed May 23 22:35:01 EDT 2007 i
+686 i686 i386 GNU/Linux
[dim@grivo out]$
[dim@grivo out]$

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In reply to Why "getlogin" not works in this case? by bdimych

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