opensnoop (8)

opensnoop [-htx] [-d secs] [-f file] [-p pid] [-n name]

This traces open() syscalls, showing the file name (pathname) and returned file descriptor number (or -1, for error).

This implementation is designed to work on older kernel versions, and without kernel debuginfo. It works by dynamic tracing of the return value of getname() as a string, and associating it with the following open() syscall return. This approach is kernel version specific, and may not work on your version. It is a workaround, and proof of concept for ftrace, until more kernel tracing functionality is available.

Since this uses ftrace, only the root user can use this tool.

FTRACE and KPROBE CONFIG, the syscalls:sys_exit_open tracepoint, and the getname() kernel function. You may already have these enabled and available on recent Linux kernels. And awk.

-d secs

Set the duration of tracing, in seconds. Trace output will be buffered and printed at the end. This also reduces overheads by buffering in-kernel, instead of printing events as they occur.

The ftrace buffer has a fixed size per-CPU (see /sys/kernel/debug/tracing/buffer_size_kb). If you think events are missing, try increasing that size.

-f file

Only show open()s which match this filename. Partial strings and regular expressions are allowed. This is post-filtered using awk.

-h

Print usage message.

-n name

Only show processes matching this process name. Partial strings and regular expressions are allowed. This is post-filtered using awk.

-p PID

Only trace this process ID. This is filtered in-kernel.

-t

Include timestamps, in seconds.

-x

Only print failed open()s.

Trace all open() syscalls with details:

opensnoop

Only trace open()s for PID 81:

opensnoop -p 81

Trace failed open() syscalls:

opensnoop -x

Trace open() syscalls for filenames containing "log":

opensnoop -f log

TIMEs

Time of open() completion, in units of seconds.

COMM

Process name (if known).

PID

Process ID.

FD

File descriptor. If this is a successful open, the file descriptor number is shown. If this is unsuccessful, -1 is shown. Numbers beginning with 0x are hexadecimal.

FILE

Filename (pathname) used by the open() syscall.

This reads and open() syscalls and getname() kernel functions as they occur. For high rates of opens (> 500/s), the overhead may begin to be measurable. Test yourself. You can use the -d mode to buffer output, reducing overheads.

This is from the perf-tools collection.

• https://github.com/brendangregg/perf-tools

Also look under the examples directory for a text file containing example usage, output, and commentary for this tool.

Linux

Unstable - in development.

Brendan Gregg

execsnoop(8), strace(1)