NAME¶

opensnoop - Trace open() syscalls. Uses Linux eBPF/bcc.

SYNOPSIS¶

opensnoop.py [-h] [-T] [-U] [-x] [-p PID] [-t TID] [-u UID]
[-d DURATION] [-n NAME] [-e] [-f FLAG_FILTER]
[--cgroupmap MAPPATH] [--mntnsmap MAPPATH]

DESCRIPTION¶

opensnoop traces the open() syscall, showing which processes are attempting to open which files. This can be useful for determining the location of config and log files, or for troubleshooting applications that are failing, specially on startup.

This works by tracing the kernel sys_open() function using dynamic tracing, and will need updating to match any changes to this function.

This makes use of a Linux 4.4 feature (bpf_perf_event_output()); for kernels older than 4.4, see the version under tools/old, which uses an older mechanism.

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

REQUIREMENTS¶

CONFIG_BPF and bcc.

OPTIONS¶

-h

Print usage message.

-T

Include a timestamp column.

-U

Show UID.

-x

Only print failed opens.

-p PID

Trace this process ID only (filtered in-kernel).

-t TID

Trace this thread ID only (filtered in-kernel).

-u UID

Trace this UID only (filtered in-kernel).

-d DURATION

Total duration of trace in seconds.

-n name

Only print processes where its name partially matches 'name'

-e

Show extended fields.

-f FLAG

Filter on open() flags, e.g., O_WRONLY.

--cgroupmap MAPPATH

Trace cgroups in this BPF map only (filtered in-kernel).

--mntnsmap MAPPATH

Trace mount namespaces in this BPF map only (filtered in-kernel).

EXAMPLES¶

Trace all open() syscalls:

# opensnoop

Trace all open() syscalls, for 10 seconds only:

# opensnoop -d 10

Trace all open() syscalls, and include timestamps:

# opensnoop -T

Show UID:

# opensnoop -U

Trace only open() syscalls that failed:

# opensnoop -x

Trace PID 181 only:

# opensnoop -p 181

Trace UID 1000 only:

# opensnoop -u 1000

Trace all open() syscalls from processes where its name partially matches 'ed':

# opensnoop -n ed

Show extended fields:

# opensnoop -e

Only print calls for writing:

# opensnoop -f O_WRONLY -f O_RDWR

Trace a set of cgroups only (see special_filtering.md from bcc sources for more details):

# opensnoop --cgroupmap /sys/fs/bpf/test01

FIELDS¶

TIME(s)

Time of the call, in seconds.

UID

User ID

PID

Process ID

TID

Thread ID

COMM

Process name

FD

File descriptor (if success), or -1 (if failed)

ERR

Error number (see the system's errno.h)

FLAGS

Flags passed to open(2), in octal

PATH

Open path

OVERHEAD¶

This traces the kernel open function and prints output for each event. As the rate of this is generally expected to be low (< 1000/s), the overhead is also expected to be negligible. If you have an application that is calling a high rate of open()s, then test and understand overhead before use.

SOURCE¶

This is from bcc.

https://github.com/iovisor/bcc

Also look in the bcc distribution for a companion _examples.txt file containing example usage, output, and commentary for this tool.

OS¶

Linux

AUTHOR¶

Brendan Gregg

SEE ALSO¶

execsnoop(8), funccount(1)