Strange error behavior

gistfile1.txt

~/dev/node (master)]$ ./node
> process.version
'v0.7.7-pre'
> var fs = require('fs')

// callback for fs.readFile
> var fn = function (err, data) { 
    if (err) return console.dir(err); 
    console.dir(data); 
  }

> fs.readFile('/proc/4682/mem', fn);
{ [Error: ESRCH, read] errno: 48, code: 'ESRCH' }

> fs.readFileSync('/proc/4682/mem');
Error: UNKNOWN, unknown error
    at Object.readSync (fs.js:316:19)
    at Object.readFileSync (fs.js:161:19)
    at repl:1:4
    at REPLServer.eval (repl.js:89:21)
    at repl.js:217:20
    at REPLServer.eval (repl.js:96:5)
    at Interface.<anonymous> (repl.js:207:12)
    at Interface.emit (events.js:67:17)
    at Interface._onLine (readline.js:164:10)
    at Interface._line (readline.js:456:8)
>