opensnoop

NAME

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

SYNOPSIS

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

-F

Show full path for an open file with relative path.

--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

STABILITY

Unstable - in development.

AUTHOR

Brendan Gregg, Rocky Xing

SEE ALSO

execsnoop(8), funccount(1)