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D(7) Miscellaneous Information Manual D(7) NAME D -- DTrace scripting language overview SYNOPSIS provider:module:function:name [[/predicate/] {action}] DESCRIPTION D is the dtrace(1) scripting language. This manual provides a brief reference of the D language and scripting. This manual page serves as a short reference of the language. Refer to books listed in "SEE ALSO" for a complete reference. PROBE'S DESCRIPTION A probe's description consists of four elements: provider:module:function:name The exact meaning of module, function, and name depends on provider. USER-DEFINED VARIABLE TYPES Type Syntax global variable_name aggregate @variable_name thread-local self->variable_name clause-local this->variable_name Tips: - Always use the variable type with the smallest scope to minimize processing overhead. - Use aggregate variables instead of global variables when possible. Aggregate variables are multi-CPU safe in contrast to global vari- ables. BUILT-IN VARIABLES Probe Arguments args[] The array of typed probe arguments. arg0, ..., arg9 The untyped probe arguments represented as 64-bit un- signed integers. Only the first ten arguments are available this way. Probe Information epid The enabled probe ID which uniquely identifies an enabled probe. An enabled probe is defined by its probe ID, its predicates, and its actions. id The probe ID which uniquely identifies a probe available to DTrace. probeprov The provider in the probe's description (provider:module:function:name) . probemod The module in the probe's description (provider:module:function:name) . probefunc The function in the probe's description (provider:module:function:name) . probename The name in the probe's description (provider:module:function:name) . Process Information execargs The process arguments. Effectively, `curthread->td_proc->p_args'. execname The name of the current process. Effectively, `curthread->td_proc->p_comm'. gid The group ID of the current process. pid The process ID of the current process. ppid The parent process ID of the current process. uid The user ID of the current process. Thread Information uregs[] The saved user-mode register values. cpu The ID of the current CPU. stackdepth The kernel stack frame depth. ustackdepth The userspace counterpart of stackdepth. tid The thread ID. Depending on the context, this can be ei- ther the ID of a kernel thread or a thread in a user process. errno The errno(2) value of the last system call performed by the current thread. curlwpsinfo A pointer to the lwpsinfo_t representation of the current thread. Refer to dtrace_proc(4) for more details. curpsinfo A pointer to the psinfo_t representation of the current process. Refer to dtrace_proc(4) for more details. curthread A pointer to the thread struct that is currently on-CPU. E.g., `curthread->td_name' returns the thread name. The <sys/proc.h> header documents all members of struct thread. caller The address of the kernel thread instruction at the time of execution of the current probe. ucaller The userspace counterpart of caller. Timestamps timestamp The number of nanoseconds since boot. Suitable for cal- culating relative time differences of elapsed time and latency. vtimestamp The number of nanoseconds that the current thread spent on CPU. The counter is not increased during handling of a fired DTrace probe. Suitable for calculating relative time differences of on-CPU time. walltimestamp The number of nanoseconds since the Epoch (1970-01-01T00+00:00). Suitable for timestamping logs. BUILT-IN FUNCTIONS string strchr(string s, char c) Return a substring of s starting at the first occurance of c in s. Return NULL if c does not occur in s. For example, strchr("abc", 'b'); returns `bc' and strchr("abc", 'd'); returns NULL. string strjoin(string s1, string s2) Return a string resulting from concatenating s1 and s2. For example, strjoin("abc", "def") returns `abcdef'. string strrchr(string s, char c) Return a substring of s starting at the last occurance of c in s. Similar to strchr(). string strstr(string haystack, string needle) Return a substring of haystack starting at the first oc- currence of needle. Return NULL if needle is not a sub- string of haystack. For example, strstr("abc1bc2", "bc") returns `bc1bc2' and strstr("abc", "xy") returns NULL. string strtok(string s, string separators) Tokenize s with separators. For example, strtok("abcdefg", "xyzd") returns `abc'. size_t strlen(string s) Return the length of string s. string substr(string s, int position, [int length]) Return a substring of string s starting at position. The substring will be at most length-long. If length is not specified, use the rest of the string. If position is greater than the size of s, return an empty string. For example, substr("abcd", 2) returns `cd', substr("abcd", 2, 1) returns `c', and substr("abcd", 99) returns an empty string. Aggregation Functions avg(value) Average count() Count llquantize(value, factor, low, high, nsteps) Log-linear quantization lquantize(value, low, high, nsteps) Linear quantization max(value) Maximum min(value) Minimum quantize(value) Power-of-two frequency distribution stddev(value) Standard deviation sum(value) Sum Kernel Destructive Functions By default, dtrace(1) does not permit the use of destructive actions. breakpoint() Set a kernel breakpoint and transfer control to the ddb(4) kernel debugger. chill(nanoseconds) Spin on the CPU for the specified number of nanoseconds. panic() Panic the kernel. FILES /usr/share/dtrace DTrace scripts shipped with FreeBSD base. SEE ALSO awk(1), dtrace(1), tracing(7) The illumos Dynamic Tracing Guide, https://illumos.org/books/dtrace/, 2008. Brendan Gregg and Jim Mauro, DTrace: Dynamic Tracing in Oracle Solaris, Mac OS X and FreeBSD, Prentice Hall, https://www.brendangregg.com/dtracebook/, 2011. George Neville-Neil, Jonathan Anderson, Graeme Jenkinson, Brian Kidney, Domagoj Stolfa, Arun Thomas, and Robert N. M. Watson, Univeristy of Cambridge Computer Laboratory, OpenDTrace Specification version 1.0, https://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-924.pdf, Cambridge, United Kingdom, August 2018. HISTORY This manual page first appeared in FreeBSD 15.0. AUTHORS This manual page was written by Mateusz Piotrowski <0mp@FreeBSD.org>. BUGS The cwd variable which typically provides the current working directory is not supported on FreeBSD at the moment. FreeBSD ports 15.quarterly October 28, 2025 D(7)
NAME | SYNOPSIS | DESCRIPTION | PROBE'S DESCRIPTION | USER-DEFINED VARIABLE TYPES | BUILT-IN VARIABLES | BUILT-IN FUNCTIONS | FILES | SEE ALSO | HISTORY | AUTHORS | BUGS
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