I have 2GiB RAM, running Perl 5.8.8 on Linux 2.6.

Whenever I open /dev/mem the call succeeds (that is I can get a filehandle on it), but also error 25 "Inappropriate ioctl for device" is returned. I don't know what that is supposed to mean. 

$ok = sysopen my $mem, '/dev/mem', O_RDWR;

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Following some suggestions in the open(2) manpage I tried to get rid of it by |ing (binary or) the mode with O_DIRECT and O_NONBLOCK and variations thereof, but it only made it worse, I get 22 "Invalid argument" and the call fails.

sysread()ing works up to address hex 38000000 (only ~896 MiB), then fails with error 14 "Bad address". Experiment from the shell supports it: 

$ sudo cat /dev/mem > memdump
cat: /dev/mem: Bad address

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However, I can successfully sysseek() to any address in the file (even though error 25 is set again).

sysread()ing from /proc/$pid/mem is totally useless, it always fails with error 3 "No such process", even though sysopen()ing and sysseek()ing do succeed.

How comes all that strange behaviour, and why is that so?

How do I know where each program is located, anyway? I had a look at /proc/$pid/maps, but it's impossible that dozens of processes occupy overlapping or even exact same space after hex 8000000. Reading from /dev/mem at that point also returns garbage, well, at least not the garbage I expect.

In reply to messing with memory by Anonymous Monk

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