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opensnoop_example.txt
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Demonstrations of opensnoop, the Linux eBPF/bcc version.
opensnoop traces the open() syscall system-wide, and prints various details.
Example output:
# ./opensnoop
PID COMM FD ERR PATH
17326 <...> 7 0 /sys/kernel/debug/tracing/trace_pipe
1576 snmpd 9 0 /proc/net/dev
1576 snmpd 11 0 /proc/net/if_inet6
1576 snmpd 11 0 /proc/sys/net/ipv4/neigh/eth0/retrans_time_ms
1576 snmpd 11 0 /proc/sys/net/ipv6/neigh/eth0/retrans_time_ms
1576 snmpd 11 0 /proc/sys/net/ipv6/conf/eth0/forwarding
1576 snmpd 11 0 /proc/sys/net/ipv6/neigh/eth0/base_reachable_time_ms
1576 snmpd 11 0 /proc/sys/net/ipv4/neigh/lo/retrans_time_ms
1576 snmpd 11 0 /proc/sys/net/ipv6/neigh/lo/retrans_time_ms
1576 snmpd 11 0 /proc/sys/net/ipv6/conf/lo/forwarding
1576 snmpd 11 0 /proc/sys/net/ipv6/neigh/lo/base_reachable_time_ms
1576 snmpd 9 0 /proc/diskstats
1576 snmpd 9 0 /proc/stat
1576 snmpd 9 0 /proc/vmstat
1956 supervise 9 0 supervise/status.new
1956 supervise 9 0 supervise/status.new
17358 run 3 0 /etc/ld.so.cache
17358 run 3 0 /lib/x86_64-linux-gnu/libtinfo.so.5
17358 run 3 0 /lib/x86_64-linux-gnu/libdl.so.2
17358 run 3 0 /lib/x86_64-linux-gnu/libc.so.6
17358 run -1 6 /dev/tty
17358 run 3 0 /proc/meminfo
17358 run 3 0 /etc/nsswitch.conf
17358 run 3 0 /etc/ld.so.cache
17358 run 3 0 /lib/x86_64-linux-gnu/libnss_compat.so.2
17358 run 3 0 /lib/x86_64-linux-gnu/libnsl.so.1
17358 run 3 0 /etc/ld.so.cache
17358 run 3 0 /lib/x86_64-linux-gnu/libnss_nis.so.2
17358 run 3 0 /lib/x86_64-linux-gnu/libnss_files.so.2
17358 run 3 0 /etc/passwd
17358 run 3 0 ./run
^C
While tracing, the snmpd process opened various /proc files (reading metrics),
and a "run" process read various libraries and config files (looks like it
was starting up: a new process).
opensnoop can be useful for discovering configuration and log files, if used
during application startup.
The -p option can be used to filter on a PID, which is filtered in-kernel. Here
I've used it with -T to print timestamps:
./opensnoop -Tp 1956
TIME(s) PID COMM FD ERR PATH
0.000000000 1956 supervise 9 0 supervise/status.new
0.000289999 1956 supervise 9 0 supervise/status.new
1.023068000 1956 supervise 9 0 supervise/status.new
1.023381997 1956 supervise 9 0 supervise/status.new
2.046030000 1956 supervise 9 0 supervise/status.new
2.046363000 1956 supervise 9 0 supervise/status.new
3.068203997 1956 supervise 9 0 supervise/status.new
3.068544999 1956 supervise 9 0 supervise/status.new
This shows the supervise process is opening the status.new file twice every
second.
The -U option include UID on output:
# ./opensnoop -U
UID PID COMM FD ERR PATH
0 27063 vminfo 5 0 /var/run/utmp
103 628 dbus-daemon -1 2 /usr/local/share/dbus-1/system-services
103 628 dbus-daemon 18 0 /usr/share/dbus-1/system-services
103 628 dbus-daemon -1 2 /lib/dbus-1/system-services
The -u option filtering UID:
# ./opensnoop -Uu 1000
UID PID COMM FD ERR PATH
1000 30240 ls 3 0 /etc/ld.so.cache
1000 30240 ls 3 0 /lib/x86_64-linux-gnu/libselinux.so.1
1000 30240 ls 3 0 /lib/x86_64-linux-gnu/libc.so.6
1000 30240 ls 3 0 /lib/x86_64-linux-gnu/libpcre.so.3
1000 30240 ls 3 0 /lib/x86_64-linux-gnu/libdl.so.2
1000 30240 ls 3 0 /lib/x86_64-linux-gnu/libpthread.so.0
The -x option only prints failed opens:
# ./opensnoop -x
PID COMM FD ERR PATH
18372 run -1 6 /dev/tty
18373 run -1 6 /dev/tty
18373 multilog -1 13 lock
18372 multilog -1 13 lock
18384 df -1 2 /usr/share/locale/en_US.UTF-8/LC_MESSAGES/coreutils.mo
18384 df -1 2 /usr/share/locale/en_US.utf8/LC_MESSAGES/coreutils.mo
18384 df -1 2 /usr/share/locale/en_US/LC_MESSAGES/coreutils.mo
18384 df -1 2 /usr/share/locale/en.UTF-8/LC_MESSAGES/coreutils.mo
18384 df -1 2 /usr/share/locale/en.utf8/LC_MESSAGES/coreutils.mo
18384 df -1 2 /usr/share/locale/en/LC_MESSAGES/coreutils.mo
18385 run -1 6 /dev/tty
18386 run -1 6 /dev/tty
This caught a df command failing to open a coreutils.mo file, and trying from
different directories.
The ERR column is the system error number. Error number 2 is ENOENT: no such
file or directory.
A maximum tracing duration can be set with the -d option. For example, to trace
for 2 seconds:
# ./opensnoop -d 2
PID COMM FD ERR PATH
2191 indicator-multi 11 0 /sys/block
2191 indicator-multi 11 0 /sys/block
2191 indicator-multi 11 0 /sys/block
2191 indicator-multi 11 0 /sys/block
2191 indicator-multi 11 0 /sys/block
The -n option can be used to filter on process name using partial matches:
# ./opensnoop -n ed
PID COMM FD ERR PATH
2679 sed 3 0 /etc/ld.so.cache
2679 sed 3 0 /lib/x86_64-linux-gnu/libselinux.so.1
2679 sed 3 0 /lib/x86_64-linux-gnu/libc.so.6
2679 sed 3 0 /lib/x86_64-linux-gnu/libpcre.so.3
2679 sed 3 0 /lib/x86_64-linux-gnu/libdl.so.2
2679 sed 3 0 /lib/x86_64-linux-gnu/libpthread.so.0
2679 sed 3 0 /proc/filesystems
2679 sed 3 0 /usr/lib/locale/locale-archive
2679 sed -1 2
2679 sed 3 0 /usr/lib/x86_64-linux-gnu/gconv/gconv-modules.cache
2679 sed 3 0 /dev/null
2680 sed 3 0 /etc/ld.so.cache
2680 sed 3 0 /lib/x86_64-linux-gnu/libselinux.so.1
2680 sed 3 0 /lib/x86_64-linux-gnu/libc.so.6
2680 sed 3 0 /lib/x86_64-linux-gnu/libpcre.so.3
2680 sed 3 0 /lib/x86_64-linux-gnu/libdl.so.2
2680 sed 3 0 /lib/x86_64-linux-gnu/libpthread.so.0
2680 sed 3 0 /proc/filesystems
2680 sed 3 0 /usr/lib/locale/locale-archive
2680 sed -1 2
^C
This caught the 'sed' command because it partially matches 'ed' that's passed
to the '-n' option.
The -e option prints out extra columns; for example, the following output
contains the flags passed to open(2), in octal:
# ./opensnoop.py -e
PID COMM FD ERR FLAGS MODE PATH
12458 open 3 0 02000000 n/a /etc/ld.so.cache
12458 open 3 0 02000000 n/a /lib/x86_64-linux-gnu/libc.so.6
12458 open 3 0 00000301 0664 tmp.txt
12459 openat 3 0 02000000 n/a /etc/ld.so.cache
12459 openat 3 0 02000000 n/a /lib/x86_64-linux-gnu/libc.so.6
12459 openat 3 0 00000301 0664 tmp.txt
12460 openat2 3 0 02000000 n/a /etc/ld.so.cache
12460 openat2 3 0 02000000 n/a /lib/x86_64-linux-gnu/libc.so.6
12460 openat2 3 0 00000000 n/a .
12460 openat2 3 0 00000000 n/a .
12460 openat2 4 0 00000000 n/a ..
The -f option filters based on flags to the open(2) call, for example:
# ./opensnoop.py -e -f O_WRONLY -f O_RDWR
PID COMM FD ERR FLAGS MODE PATH
12540 open 3 0 00000301 0664 tmp.txt
12541 openat 3 0 00000301 0664 tmp.txt
9039 openat 3 0 00000301 0000 tmp.txt
The --cgroupmap option filters based on a cgroup set. It is meant to be used
with an externally created map.
# ./opensnoop --cgroupmap /sys/fs/bpf/test01
For more details, see docs/special_filtering.md
USAGE message:
# ./opensnoop -h
usage: opensnoop.py [-h] [-T] [-U] [-x] [-p PID] [-t TID]
[--cgroupmap CGROUPMAP] [--mntnsmap MNTNSMAP] [-u UID]
[-d DURATION] [-n NAME] [-e] [-f FLAG_FILTER] [-F]
[-b BUFFER_PAGES]
Trace open() syscalls
optional arguments:
-h, --help show this help message and exit
-T, --timestamp include timestamp on output
-U, --print-uid print UID column
-x, --failed only show failed opens
-p PID, --pid PID trace this PID only
-t TID, --tid TID trace this TID only
--cgroupmap CGROUPMAP
trace cgroups in this BPF map only
--mntnsmap MNTNSMAP trace mount namespaces in this BPF map only
-u UID, --uid UID trace this UID only
-d DURATION, --duration DURATION
total duration of trace in seconds
-n NAME, --name NAME only print process names containing this name
-e, --extended_fields
show extended fields
-f FLAG_FILTER, --flag_filter FLAG_FILTER
filter on flags argument (e.g., O_WRONLY)
-F, --full-path show full path for an open file with relative path
-b BUFFER_PAGES, --buffer-pages BUFFER_PAGES
size of the perf ring buffer (must be a power of two
number of pages and defaults to 64)
examples:
./opensnoop # trace all open() syscalls
./opensnoop -T # include timestamps
./opensnoop -U # include UID
./opensnoop -x # only show failed opens
./opensnoop -p 181 # only trace PID 181
./opensnoop -t 123 # only trace TID 123
./opensnoop -u 1000 # only trace UID 1000
./opensnoop -d 10 # trace for 10 seconds only
./opensnoop -n main # only print process names containing "main"
./opensnoop -e # show extended fields
./opensnoop -f O_WRONLY -f O_RDWR # only print calls for writing
./opensnoop -F # show full path for an open file with relative path
./opensnoop --cgroupmap mappath # only trace cgroups in this BPF map
./opensnoop --mntnsmap mappath # only trace mount namespaces in the map