How to detect a memory leak?

Question 1

I seem to have a larger memory leak on my current ubuntu System

After reporting strange Eclipse memory errors ( https://askubuntu.com/questions/148998/eclipse-constant-different-out-of-memory-errors ) I started to get ‘Not enough Memory’ error messages in my console today – while doing simple tasks like typing in sudo -s – or even – free -m

Typing in ‘free -m’ repeadetly showed me how my RAM quickly goes up from 700M to 900M, growing up to the size of 2000M in a few seconds (after freeing up memory with echo 3 > /proc/sys/vm/drop_caches )

Eclipse isnt the cause, I completly killed the process and the ram still was going up. Is there any way to detect where the leak is coming from? I cant even update my system anymore, since apt-get update fails (probably because it’s out of memory)

Using Ubuntu 11.10

Question 2

First, make sure to have a temp folder available which has enough free space. The following commands create dumps which can be several GBs in size.

You can create a new tmp folder using the following command. You may want to change /tmp to a different filesystem with enough space

TMPDIR=$(mktemp -d -t -p /tmp)

Steps to find Memory Leak

Find out the PID of the process which causing memory leak (you can also use e.g. htop if available) and store it in a variable called pid
```
ps -aux
```
Given that the PID is available in the variable pid, you can capture the memory consumption using /proc/$pid/smaps and save into some file like beforeMemInc.txt.
```
cat /proc/$pid/smaps > $TMPDIR/beforeMemInc.txt
```
Wait some time for memory consumption to increase.
Capture /proc/$pid/smaps again and save it as afterMemInc.txt
```
cat /proc/$pid/smaps > $TMPDIR/afterMemInc.txt
```
Find the difference between first smaps and 2nd smaps, e. g. with
```
diff -u $TMPDIR/beforeMemInc.txt $TMPDIR/afterMemInc.txt
```

Note down the address range where memory got increased, for example:

   beforeMemInc.txt            afterMemInc.txt
---------------------------------------------------
2b3289290000-2b3289343000   2b3289290000-2b3289343000  #ADDRESS
Shared_Clean:    0 kB       Shared_Clean:    0 kB          
Shared_Dirty:    0 kB       Shared_Dirty:    0 kB
Private_Clean:   0 kB       Private_Clean:   0 kB
Private_Dirty:  28 kB       Private_Dirty:  36 kB  
Referenced:     28 kB       Referenced:     36 kB
Anonymous:      28 kB       Anonymous:      36 kB  #INCREASE MEM
AnonHugePages:   0 kB       AnonHugePages:   0 kB
Swap:            0 kB       Swap:            0 kB
KernelPageSize:  4 kB       KernelPageSize:  4 kB
MMUPageSize:     4 kB       MMUPageSize:     4 kB
Locked:          0 kB       Locked:          0 kB
VmFlags: rd wr mr mw me ac  VmFlags: rd wr mr mw me ac

Use GDB to dump memory on running process or get the coredump using
```
gcore -o $TMPDIR/process $PID
```

I used gdb on the running process to dump the memory to some file.

cd $TMPDIR
gdb -p $pid
dump memory memory.dump 0x2b3289290000 0x2b3289343000

Now, use strings command or hexdump -C to print the memory.dump
```
strings memory.dump
```
From this you get readable information which helps you locate those strings in your source code.
Analyse your source to find the leak.

How to detect a memory leak?

Answer

Steps to find Memory Leak

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