test

DTrace User Guide

syscall Provider

The syscall provider enables you to trace every system call entry and return. You can use the prstat(1M) command to see examine process behavior.


$ prstat -m -p 31337
   PID USERNAME USR SYS TRP TFL DFL LCK SLP LAT VCX ICX SCL SIG PROCESS/NLWP  
 13499 user1     53  44 0.0 0.0 0.0 0.0 2.5 0.0  4K  24  9K   0 mystery/6

This example shows that the process is consuming a large amount of system time. One possible explanation for this behavior is that the process is executing a large number of system calls. You can use a simple D program specified on the command line to see which system calls are happening most often:


# dtrace -n syscall:::entry'/pid == 31337/{ @syscalls[probefunc] = count(); }'
dtrace: description 'syscall:::entry' matched 215 probes
^C

  open                                                              1
  lwp_park                                                          2
  times                                                             4
  fcntl                                                             5
  close                                                             6
  sigaction                                                         6
  read                                                             10
  ioctl                                                            14
  sigprocmask                                                     106
  write                                                          1092

This report shows a large number of system calls to the write() function. You can use the syscall provider to further examine the source of all the write() system calls:


# dtrace -n syscall::write:entry'/pid == 31337/{ @writes[arg2] = quantize(); }'
dtrace: description 'syscall::write:entry' matched 1 probe
^C

           value  ------------- Distribution ------------- count    
               0 |                                         0        
               1 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@   1037
               2 |@                                        3        
               4 |                                         0        
               8 |                                         0        
              16 |                                         0        
              32 |@                                        3        
              64 |                                         0        
             128 |                                         0        
             256 |                                         0        
             512 |                                         0        
            1024 |@                                        5        
            2048 |                                         0

The output shows that the process is executing many write() system calls with a relatively small amount of data.