.\" $FreeBSD$
.\"
.Dd May 12, 2009
.Dt TRUSS 1
.Os
.Sh NAME
.Nm truss
.Nd trace system calls
.Sh SYNOPSIS
.Nm
.Op Fl facedDS
.Op Fl o Ar file
.Op Fl s Ar strsize
.Fl p Ar pid
.Nm
.Op Fl facedDS
.Op Fl o Ar file
.Op Fl s Ar strsize
.Ar command Op Ar args
.Sh DESCRIPTION
The
.Nm
utility traces the system calls called by the specified process or program.
Output is to the specified output file, or standard error by default.
It does this by stopping and restarting the process being monitored via
.Xr ptrace 2 .
.Pp
The options are as follows:
.Bl -tag -width indent
.It Fl f
Trace descendants of the original traced process created by
.Xr fork 2 ,
.Xr vfork 2 ,
etc.
.It Fl a
Show the argument strings that are passed in each
.Xr execve 2
system call.
.It Fl c
Do not display individual system calls.
Instead, before exiting, print a summary containing for each system call:
the total system time used,
the number of times the call was invoked,
and the number of times the call returned with an error.
.It Fl e
Show the environment strings that are passed in each
.Xr execve 2
system call.
.It Fl d
Include timestamps in the output showing the time elapsed
since the trace was started.
.It Fl D
Include timestamps in the output showing the time elapsed
since the last recorded event.
.It Fl S
Do not display information about signals received by the process.
(Normally,
.Nm
displays signal as well as system call events.)
.It Fl o Ar file
Print the output to the specified
.Ar file
instead of standard error.
.It Fl s Ar strsize
Display strings using at most
.Ar strsize
characters.
If the buffer is larger,
.Dq Li ...
will be displayed at the end of the string.
The default
.Ar strsize
is 32.
.It Fl p Ar pid
Follow the process specified by
.Ar pid
instead of a new command.
.It Ar command Op Ar args
Execute
.Ar command
and trace the system calls of it.
(The
.Fl p
and
.Ar command
options are mutually exclusive.)
.El
.Sh EXAMPLES
# Follow the system calls used in echoing "hello"
.Dl $ truss /bin/echo hello
# Do the same, but put the output into a file
.Dl $ truss -o /tmp/truss.out /bin/echo hello
# Follow an already-running process
.Dl $ truss -p 34
.Sh SEE ALSO
.Xr kdump 1 ,
.Xr ktrace 1 ,
.Xr ptrace 2
.Sh HISTORY
The
.Nm
command was written by
.An Sean Eric Fagan
for
.Fx .
It was modeled after
similar commands available for System V Release 4 and SunOS.