bpftrace man page

bpftrace — the eBPF tracing language & frontend

Synopsis

bpftrace [Options] FILE bpftrace [Options] -e ´program code´

Description

bpftrace is a high-level tracing language for Linux enhanced Berkeley Packet Filter (eBPF) available in recent Linux kernels (4.x).

bpftrace uses:

LLVM as a backend to compile scripts to BPF-bytecode
BCC for interacting with the Linux BPF system

As well as the existing Linux tracing capabilities:

	kernel	userland
static	tracepoints	USDT* probes
dynamic	kprobes	uprobes

*USDT = user-level statically defined tracing

The bpftrace language is inspired by awk and C, and predecessor tracers such as DTrace and SystemTap.

See Examples and Oneliners if you are impatient.
See Probe Types and Builtins (variables/functions) for the bpftrace language elements.

Options

-l [searchterm]: List probes.
-e ´PROGRAM´: Execute PROGRAM.
-p PID: Enable USDT probes on PID. Will terminate bpftrace on PID termination. Note this is not a global PID filter on probes.
-c CMD: Helper to run CMD. Equivalent to manually running CMD and then giving passing the PID to -p. This is useful to ensure you've traced at least the duration CMD's execution.
--unsafe: Enable unsafe builtin functions. By default, bpftrace runs in safe mode. Safe mode ensure programs cannot modify system state. Unsafe builtin functions are marked as such in Builtins (functions).
-v: Verbose messages.
-d: Debug info on dry run.
-dd: Verbose debug info on dry run.

Examples

bpftrace -l ´*sleep*´: List probes containing "sleep".
bpftrace -e ´kprobe:do_nanosleep { printf("PID %d sleeping\n", pid); }´: Trace processes calling sleep.
bpftrace -c ´sleep 5´ -e ´kprobe:do_nanosleep { printf("PID %d sleeping\n", pid); }´: run "sleep 5" in a new process and then trace processes calling sleep.
bpftrace -e ´tracepoint:raw_syscalls:sys_enter { @[comm]=count(); }´: Count syscalls by process name.

Oneliners

For brevity, just the the actual BPF code is shown below.
Usage: bpftrace -e ´bpf-code´

New processes with arguments:: tracepoint:syscalls:sys_enter_execve { join(args->argv); }
Files opened by process:: tracepoint:syscalls:sys_enter_open { printf("%s %s\n", comm, str(args->filename)); }
Syscall count by program:: tracepoint:raw_syscalls:sys_enter { @[comm] = count(); }
Syscall count by syscall:: tracepoint:syscalls:sys_enter_* { @[probe] = count(); }
Syscall count by process:: tracepoint:raw_syscalls:sys_enter { @[pid, comm] = count(); }
Read bytes by process:: tracepoint:syscalls:sys_exit_read /args->ret/ { @[comm] = sum(args->ret); }
Read size distribution by process:: tracepoint:syscalls:sys_exit_read { @[comm] = hist(args->ret); }
Disk size by process:: tracepoint:block:block_rq_issue { printf("%d %s %d\n", pid, comm, args->bytes); }
Pages paged in by process:: software:major-faults:1 { @[comm] = count(); }
Page faults by process:: software:faults:1 { @[comm] = count(); }
Profile user-level stacks at 99 Hertz, for PID 189:: profile:hz:99 /pid == 189/ { @[ustack] = count(); }

Probe Types

Kprobes

Attach a bpftrace script to a kernel function, to be executed when that function is called:

kprobe:vfs_read { ... }

Uprobes

Attach script to a userland function:

uprobe:/bin/bash:readline { ... }

Tracepoints

Attach script to a statically defined tracepoint in the kernel:

tracepoint:sched:sched_switch { ... }

Tracepoints are guaranteed to be stable between kernel versions, unlike kprobes.

Software

Attach script to kernel software events, executing once every provided count or use a default:

software:faults:100 software:faults:

Hardware

Attach script to hardware events (PMCs), executing once every provided count or use a default:

hardware:cache-references:1000000 hardware:cache-references:

Profile

Run the script on all CPUs at specified time intervals:

profile:hz:99 { ... }

profile:s:1 { ... }

profile:ms:20 { ... }

profile:us:1500 { ... }

Interval

Run the script once per interval, for printing interval output:

interval:s:1 { ... }

interval:ms:20 { ... }

Multiple Attachment Points

A single probe can be attached to multiple events:

kprobe:vfs_read,kprobe:vfs_write { ... }

Wildcards

Some probe types allow wildcards to be used when attaching a probe:

kprobe:vfs_* { ... }

Predicates

Define conditions for which a probe should be executed:

kprobe:sys_open / uid == 0 / { ... }

Builtins

The following variables and functions are available for use in bpftrace scripts:

Variables

pid: Process ID (kernel tgid)
tid: Thread ID (kernel pid)
cgroup: Cgroup ID of the current process
uid: User ID
gid: Group ID
nsecs: Nanosecond timestamp
cpu: Processor ID
comm: Process name
kstack: Kernel stack trace
ustack: User stack trace
arg0, arg1, ... etc.: Arguments to the function being traced
retval: Return value from function being traced
func: Name of the function currently being traced
probe: Full name of the probe
curtask: Current task_struct as a u64.
rand: Random number of type u32.

Functions

hist(int n): Produce a log2 histogram of values of n
lhist(int n, int min, int max, int step): Produce a linear histogram of values of n
count(): Count the number of times this function is called
sum(int n): Sum this value
min(int n): Record the minimum value seen
max(int n): Record the maximum value seen
avg(int n): Average this value
stats(int n): Return the count, average, and total for this value
delete(@x): Delete the map element passed in as an argument
str(char *s): Returns the string pointed to by s
printf(char *fmt, ...): Print formatted to stdout
print(@x[, int top [, int div]]): Print a map, with optional top entry count and divisor
clear(@x): Delete all key/values from a map
sym(void *p): Resolve kernel address
usym(void *p): Resolve user space address
kaddr(char *name): Resolve kernel symbol name
uaddr(char *name): Resolve user space symbol name
reg(char *name): Returns the value stored in the named register
join(char *arr[]): Prints the string array
time(char *fmt): Print the current time
cat(char *filename): Print file content
ntop([int af, ]int|char[4|16] addr): Convert IP address data to text
system(char *fmt) (unsafe): Execute shell command
exit(): Quit bpftrace
kstack([StackMode mode, ][int level]): Kernel stack trace
ustack([StackMode mode, ][int level]): User stack trace

History

The first official talk by Alastair on bpftrace happened at the Tracing Summit in Edinburgh, Oct 25th 2018.

Author

Created by Alastair Robertson.
Manpage by Stephan Schuberth.

Contributing

Prior to contributing new tools, read the official checklist at:
https://github.com/iovisor/bpftrace/blob/master/CONTRIBUTING-TOOLS.md

Info

October 2018