51

Is it possible to dump the current memory allocated for a process (by PID) to a file? Or read it somehow?

45

I'm not sure how you dump all the memory to a file without doing this repeatedly (if anyone knows an automated way to get gdb to do this please let me know), but the following works for any one batch of memory assuming you know the pid:

$ cat /proc/[pid]/maps

This will be in the format (example):

00400000-00421000 r-xp 00000000 08:01 592398                             /usr/libexec/dovecot/pop3-login
00621000-00622000 rw-p 00021000 08:01 592398                             /usr/libexec/dovecot/pop3-login
00622000-0066a000 rw-p 00622000 00:00 0                                  [heap]
3e73200000-3e7321c000 r-xp 00000000 08:01 229378                         /lib64/ld-2.5.so
3e7341b000-3e7341c000 r--p 0001b000 08:01 229378                         /lib64/ld-2.5.so

Pick one batch of memory (so for example 00621000-00622000) then use gdb as root to attach to the process and dump that memory:

$ gdb --pid [pid]
(gdb) dump memory /root/output 0x00621000 0x00622000

Then analyse /root/output with the strings command, less you want the PuTTY all over your screen.

  • 1
    Is there a way of doing this in just bash/sh without gdb? – Programming4life Mar 25 '17 at 5:35
  • 3
    @Programming4life gcore(1) – julian Apr 22 '17 at 12:59
49

I've made a script that accomplishes this task.

The idea commes from James Lawrie's answer and this post: http://www.linuxforums.org/forum/programming-scripting/52375-reading-memory-other-processes.html#post287195

#!/bin/bash

grep rw-p /proc/$1/maps \
| sed -n 's/^\([0-9a-f]*\)-\([0-9a-f]*\) .*$/\1 \2/p' \
| while read start stop; do \
    gdb --batch --pid $1 -ex \
        "dump memory $1-$start-$stop.dump 0x$start 0x$stop"; \
done

put this in a file (eg. "dump-all-memory-of-pid.sh") and make it executable

usage: ./dump-all-memory-of-pid.sh [pid]

The output is printed to files with the names: pid-startaddress-stopaddress.dump

Dependencies: gdb

  • 2
    Awesome! Just used it to discover which script a mysterious bash instance was running. – Tobia Jul 26 '16 at 17:02
  • Why are you only grepping for and dumpying ranges with rw-p permissions? – mxmlnkn Aug 4 at 18:45
  • @mxmlnkn That's data (rw-p), the other ranges are for code (r-xp). If you want a dump of both, then go ahead and exchange grep for e.g. cat. – A. Nilsson Aug 5 at 14:55
39

try

    gcore $pid

where $pid is the actual number of the pid; for more info see: info gcore

may take some time for the dump to happen, and some memory may not be readable, but is good enough... be aware also that it can create big files, I just created a 2GB file that way..

  • 1
    Is gcore dumping a sparse file? – CMCDragonkai Jul 30 '16 at 7:02
3

man proc says :

/proc/[pid]/mem This file can be used to access the pages of a process's memory through open(2), read(2), and lseek(2).

Maybe it can help you

  • 1
    That's not sufficient, reading another process needs a combination of /proc/<pid>/{mem,*maps}, ptrace, and some signal handling to avoid hanging the target process. – Tobu Mar 19 '13 at 10:57
  • @Tobu Indeed. I wrote a proof-of-concept script. – Gilles Jan 15 '14 at 9:18
3

I made my own program to dump the entire process memory as well, it's in C so it can be cross-compiled to Android, which is what I needed.

You can also specify IP address and tcp port. Source code here.

2

Pure bash solution:

procdump () 
{ 
    cat /proc/$1/maps | grep "rw-p" | awk '{print $1}' | ( IFS="-"
    while read a b; do
        count=$(( bd-ad ))
        ad=$(printf "%llu" "0x$a")
        bd=$(printf "%llu" "0x$b")
        dd if=/proc/$1/mem bs=1 skip=$ad count=$count of=$1_mem_$a.bin
    done )
}

Usage: procdump PID

for a cleaner dump:

procdump () 
{ 
    cat /proc/$1/maps | grep -Fv ".so" | grep " 0 " | awk '{print $1}' | ( IFS="-"
    while read a b; do
        ad=$(printf "%llu" "0x$a")
        bd=$(printf "%llu" "0x$b")
        dd if=/proc/$1/mem bs=1 skip=$ad count=$(( bd-ad )) of=$1_mem_$a.bin
    done )
}
  • So, from what I understand, the idea behind the cleaner dump is that only in-memory files have a size attached to the memory region in contrast to actual application memory, which has size 0 (as the size actually used size is unknown by the OS). – mxmlnkn Aug 4 at 19:04
  • One issue I have with this script is that the blocksize of 1 leads to a bandwidth of unacceptably slow ~30kB/s compared to using a blocksize equal to the page size (4096 for me) for which I get ~100MB/s! See here. getconf PAGESIZE is used to get the page size and then the addresses and counts are divided by it. – mxmlnkn Aug 4 at 19:30
1

Tool to dump process to standard output, pcat/memdump:

  • This one is obsolete (removed at maintainer's request); I installed the old package anyway and it failed with "Input/output error; did you use GCC with another machine's header files?". – Tobu Mar 19 '13 at 11:14
0

You can now use procdump from SysInternals suite on Linux:

https://github.com/Microsoft/ProcDump-for-Linux

0

If you want to dump a separate memory segment of the running process without creating huge core file (say with gcore), you can use a small tool from here. There is also one-liner in README if you wish to dump all readable segments into separate files.

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