Python read Linux memory process error (/proc/$pid/mem)

Question

I have the following code tested on some Linux distros (Debian, Linux Mint...) and working, but under CentOS I get an error even I run it as root: ``` #!/usr/bin/env python import re maps_file = open("/proc/18396/maps", 'r') mem_file = open("/proc/18396/mem", 'r', 0) for line in maps_file.readlines(): # for each mapped region m = re.match(r'([0-9A-Fa-f]+)-([0-9A-Fa-f]+) ([-r])', line) if m.group(3) == 'r': # if this is a readable region start = int(m.group(1), 16) end = int(m.group(2), 16) mem_file.seek(start) # seek to region start chunk = mem_file.read(end - start) # read region contents print chunk, # dump contents to standard output maps_file.close() mem_file.close() ``` The script reads the process' memory and dumps the readable region. Under CentOS 5.4 x64 I get the following error: ``` Traceback (most recent call last): File "./mem.py", line 11, in ? chunk = mem_file.read(end - start) # read region contents IOError: [Errno 3] No such process ``` The process is alive and readabl…

Accepted Answer

Found the answer myself after some digging:

```
#!/usr/bin/env python
import ctypes, re, sys

## Partial interface to ptrace(2), only for PTRACE_ATTACH and PTRACE_DETACH.
c_ptrace = ctypes.CDLL("libc.so.6").ptrace
c_pid_t = ctypes.c_int32 # This assumes pid_t is int32_t
c_ptrace.argtypes = [ctypes.c_int, c_pid_t, ctypes.c_void_p, ctypes.c_void_p]
def ptrace(attach, pid):
    op = ctypes.c_int(16 if attach else 17) #PTRACE_ATTACH or PTRACE_DETACH
    c_pid = c_pid_t(pid)
    null = ctypes.c_void_p()
    err = c_ptrace(op, c_pid, null, null)
    if err != 0: raise SysError, 'ptrace', err

pid = "18396"

ptrace(True, int(pid))
maps_file = open("/proc/"+pid+"/maps", 'r')
mem_file = open("/proc/"+pid+"/mem", 'r', 0)
for line in maps_file.readlines():  # for each mapped region
    m = re.match(r'([0-9A-Fa-f]+)-([0-9A-Fa-f]+) ([-r])', line)
    if m.group(3) == 'r':  # if this is a readable region
        start = int(m.group(1), 16)
        end = int(m.group(2), 16)
        mem_file.seek(start)  # seek to region start
        chunk = mem_file.read(end - start)  # read region contents
        print chunk,  # dump contents to standard output
maps_file.close()
mem_file.close()
ptrace(False, int(pid))
```

Python read Linux memory process error (/proc/$pid/mem)

Solution

Problem