.TH stacksnoop 8  "2016-01-14" "USER COMMANDS"
.SH NAME
stacksnoop \- Print kernel stack traces for kernel functions. Uses Linux eBPF/bcc.
.SH SYNOPSIS
.B stacksnoop [\-h] [\-p PID] [\-s] [\-v] function
.SH DESCRIPTION
stacksnoop traces a given kernel function and for each call, prints the
kernel stack back trace for that call. This shows the ancestry of function
calls, and is a quick way to investigate low frequency kernel functions and
their cause. For high frequency kernel functions, see stackcount.

This tool only works on Linux 4.6+. Stack traces are obtained using the new BPF_STACK_TRACE` APIs.
For kernels older than 4.6, see the version under tools/old.
.SH REQUIREMENTS
CONFIG_BPF and bcc.
.SH OPTIONS
.TP
\-h
Print usage message.
.TP
\-s
Show address offsets.
.TP
\-v
Print more fields.
.TP
\-p PID
Trace this process ID only (filtered in-kernel).
.TP
function
Kernel function name.
.SH EXAMPLES
.TP
Print kernel stack traces for each call to ext4_sync_fs:
#
.B stacksnoop ext4_sync_fs
.TP
Also show the symbol offsets:
#
.B stacksnoop -s ext4_sync_fs
.TP
Show extra columns:
#
.B stacksnoop -v ext4_sync_fs
.TP
Only trace when PID 185 is on-CPU:
#
.B stacksnoop -p 185 ext4_sync_fs
.SH FIELDS
.TP
TIME(s)
Time of the call, in seconds.
.TP
STACK
Kernel stack trace. The first column shows "ip" for instruction pointer, and
"r#" for each return pointer in the stack. The second column is the stack trace
as hexadecimal. The third column is the translated kernel symbol names.
.SH OVERHEAD
This can have significant overhead if frequently called functions (> 1000/s) are
traced, and is only intended for low frequency function calls. This is because
details including the stack trace for every call is passed to user space and
processed. See stackcount for higher frequency calls, which performs in-kernel
summaries.
.SH SOURCE
This is from bcc.
.IP
https://github.com/iovisor/bcc
.PP
Also look in the bcc distribution for a companion _examples.txt file containing
example usage, output, and commentary for this tool.
.SH OS
Linux
.SH STABILITY
Unstable - in development.
.SH AUTHOR
Brendan Gregg
.SH SEE ALSO
stackcount(8)