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bcc-ucalls - Man Page

Summarize method calls from high-level languages and Linux syscalls.


javacalls [-h] [-T TOP] [-L] [-S] [-v] [-m] pid [interval]
perlcalls [-h] [-T TOP] [-L] [-S] [-v] [-m] pid [interval]
phpcalls [-h] [-T TOP] [-L] [-S] [-v] [-m] pid [interval]
pythoncalls [-h] [-T TOP] [-L] [-S] [-v] [-m] pid [interval]
rubycalls [-h] [-T TOP] [-L] [-S] [-v] [-m] pid [interval]
tclcalls [-h] [-T TOP] [-L] [-S] [-v] [-m] pid [interval]
ucalls [-l {java,perl,php,python,ruby}] [-h] [-T TOP] [-L] [-S] [-v] [-m] pid [interval]


This tool summarizes method calls from high-level languages such as Java, Perl, PHP, Python, Ruby, and Tcl. It can also trace Linux system calls. Whenever a method is invoked, ucalls records the call count and optionally the method's execution time (latency) and displays a summary.

This uses in-kernel eBPF maps to store per process summaries for efficiency.

This tool relies on USDT probes embedded in many high-level languages, such as Java, Perl, PHP, Python, Ruby, and Tcl. It requires a runtime instrumented with these probes, which in some cases requires building from source with a USDT-specific flag, such as "--enable-dtrace" or "--with-dtrace". For Java, method probes are not enabled by default, and can be turned on by running the Java process with the "-XX:+ExtendedDTraceProbes" flag. For PHP processes, the environment variable USE_ZEND_DTRACE must be set to 1.

Since this uses BPF, only the root user can use this tool.


CONFIG_BPF and bcc.


-l {java,perl,php,python,ruby,tcl}

The language to trace. If not provided, only syscalls are traced (when the -S option is used).


Print only the top methods by frequency or latency.


Collect method invocation latency (duration).


Collect Linux syscalls frequency and timing.


Print the resulting BPF program, for debugging purposes.


Print times in milliseconds (the default is microseconds).


The process id to trace.


Print summary after this number of seconds and then exit. By default, wait for Ctrl+C to terminate.


Trace the top 10 Ruby method calls:

# ucalls -T 10 -l ruby 1344

Trace Python method calls and Linux syscalls including latency in milliseconds:

# ucalls -l python -mL 2020

Trace only syscalls and print a summary after 10 seconds:

# ucalls -S 788 10


Tracing individual method calls will produce a considerable overhead in all high-level languages. For languages with just-in-time compilation, such as Java, the overhead can be more considerable than for interpreted languages. On the other hand, syscall tracing will typically be tolerable for most processes, unless they have a very unusual rate of system calls.


This is from bcc.


Also look in the bcc distribution for a companion _example.txt file containing example usage, output, and commentary for this tool.




Unstable - in development.


Sasha Goldshtein

See Also

ustat(8), argdist(8)

Referenced By

The man pages bcc-javacalls(8), bcc-perlcalls(8), bcc-phpcalls(8), bcc-pythoncalls(8), bcc-rubycalls(8) and bcc-tclcalls(8) are aliases of bcc-ucalls(8).

2018-10-09 USER COMMANDS