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 -e PID COMM FD ERR FLAGS PATH 28512 sshd 10 0 00101101 /proc/self/oom_score_adj 28512 sshd 3 0 02100000 /etc/ld.so.cache 28512 sshd 3 0 02100000 /lib/x86_64-linux-gnu/libwrap.so.0 28512 sshd 3 0 02100000 /lib/x86_64-linux-gnu/libaudit.so.1 28512 sshd 3 0 02100000 /lib/x86_64-linux-gnu/libpam.so.0 28512 sshd 3 0 02100000 /lib/x86_64-linux-gnu/libselinux.so.1 28512 sshd 3 0 02100000 /lib/x86_64-linux-gnu/libsystemd.so.0 28512 sshd 3 0 02100000 /usr/lib/x86_64-linux-gnu/libcrypto.so.1.0.2 28512 sshd 3 0 02100000 /lib/x86_64-linux-gnu/libutil.so.1 The -f option filters based on flags to the open(2) call, for example: # ./opensnoop -e -f O_WRONLY -f O_RDWR PID COMM FD ERR FLAGS PATH 28084 clear_console 3 0 00100002 /dev/tty 28084 clear_console -1 13 00100002 /dev/tty0 28084 clear_console -1 13 00100001 /dev/tty0 28084 clear_console -1 13 00100002 /dev/console 28084 clear_console -1 13 00100001 /dev/console 28051 sshd 8 0 02100002 /var/run/utmp 28051 sshd 7 0 00100001 /var/log/wtmp USAGE message: # ./opensnoop -h usage: opensnoop [-h] [-T] [-x] [-p PID] [-t TID] [-d DURATION] [-n NAME] [-e] [-f FLAG_FILTER] Trace open() syscalls optional arguments: -h, --help show this help message and exit -T, --timestamp include timestamp on output -U, --print-uid include UID on output -x, --failed only show failed opens -p PID, --pid PID trace this PID only -t TID, --tid TID trace this TID 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) 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