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KTRACE(2) FreeBSD System Calls Manual KTRACE(2)
NAME
ktrace - process tracing
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/param.h>
#include <sys/time.h>
#include <sys/uio.h>
#include <sys/ktrace.h>
int
ktrace(const char *tracefile, int ops, int trpoints, int pid);
DESCRIPTION
The ktrace() system call enables or disables tracing of one or more
processes. Users may only trace their own processes. Only the super-
user can trace setuid or setgid programs.
The tracefile argument gives the pathname of the file to be used for
tracing. The file must exist and be a regular file writable by the
calling process. All trace records are always appended to the file, so
the file must be truncated to zero length to discard previous trace data.
If tracing points are being disabled (see KTROP_CLEAR below), tracefile
may be NULL.
The ops argument specifies the requested ktrace operation. The defined
operations are:
KTROP_SET Enable trace points specified in trpoints.
KTROP_CLEAR Disable trace points specified in trpoints.
KTROP_CLEARFILE Stop all tracing.
KTRFLAG_DESCEND The tracing change should apply to the
specified process and all its current
children.
The trpoints argument specifies the trace points of interest. The
defined trace points are:
KTRFAC_SYSCALL Trace system calls.
KTRFAC_SYSRET Trace return values from system calls.
KTRFAC_NAMEI Trace name lookup operations.
KTRFAC_GENIO Trace all I/O (note that this option can
generate much output).
KTRFAC_PSIG Trace posted signals.
KTRFAC_CSW Trace context switch points.
KTRFAC_USER Trace application-specific events.
KTRFAC_STRUCT Trace certain data structures.
KTRFAC_SYSCTL Trace sysctls.
KTRFAC_PROCCTOR Trace process construction.
KTRFAC_PROCDTOR Trace process destruction.
KTRFAC_CAPFAIL Trace capability failures.
KTRFAC_FAULT Trace page faults.
KTRFAC_FAULTEND Trace the end of page faults.
KTRFAC_STRUCT_ARRAY Trace arrays of certain data structures.
KTRFAC_INHERIT Inherit tracing to future children.
pid_t ktr_pid; /* process id */
char ktr_comm[MAXCOMLEN+1]; /* command name */
struct timeval ktr_time; /* timestamp */
long ktr_tid; /* thread id */
};
The ktr_len field specifies the length of the ktr_type data that follows
this header. The ktr_pid and ktr_comm fields specify the process and
command generating the record. The ktr_time field gives the time (with
microsecond resolution) that the record was generated. The ktr_tid field
holds a thread id.
The generic header is followed by ktr_len bytes of a ktr_type record.
The type specific records are defined in the <sys/ktrace.h> include file.
SYSCTL TUNABLES
The following sysctl(8) tunables influence the behaviour of ktrace():
kern.ktrace.genio_size
bounds the amount of data a traced I/O request will log to the
trace file.
kern.ktrace.request_pool
bounds the number of trace events being logged at a time.
Sysctl tunables that control process debuggability (as determined by
p_candebug(9)) also affect the operation of ktrace().
RETURN VALUES
The ktrace() function returns the value 0 if successful; otherwise the
value -1 is returned and the global variable errno is set to indicate the
error.
ERRORS
The ktrace() system call will fail if:
[ENOTDIR] A component of the path prefix is not a directory.
[ENAMETOOLONG] A component of a pathname exceeded 255 characters, or
an entire path name exceeded 1023 characters.
[ENOENT] The named tracefile does not exist.
[EACCES] Search permission is denied for a component of the
path prefix.
[ELOOP] Too many symbolic links were encountered in
translating the pathname.
[EIO] An I/O error occurred while reading from or writing to
the file system.
[EINTEGRITY] Corrupted data was detected while reading from the
file system.
[ENOSYS] The kernel was not compiled with ktrace support.
A thread may be unable to log one or more tracing events due to a
temporary shortage of resources. This condition is remembered by the
The ktrace() system call first appeared in 4.4BSD.
FreeBSD 14.0-RELEASE-p11 November 2, 2022 FreeBSD 14.0-RELEASE-p11