Show Table of Contents
8.2. Using strace
To run the
strace utility on a program you want to analyze, type the following at a shell prompt:
scl enable devtoolset-6 'strace program [argument...]'
Replace program with the name of the program you want to analyze, and argument with any command line options and arguments you want to supply to this program. Alternatively, you can run the utility on an already running process by using the
-p command line option followed by the process ID:
scl enable devtoolset-6 'strace -p process_id'
Note that you can execute any command using the
scl utility, causing it to be run with the Red Hat Developer Toolset binaries used in preference to the Red Hat Enterprise Linux system equivalent. This allows you to run a shell session with Red Hat Developer Toolset strace as default:
scl enable devtoolset-6 'bash'Note
To verify the version of
strace you are using at any point, type the following at a shell prompt:
which strace
Red Hat Developer Toolset's
strace executable path will begin with /opt. Alternatively, you can use the following command to confirm that the version number matches that for Red Hat Developer Toolset strace:
strace -V8.2.1. Redirecting Output to a File
By default,
strace prints the name of each system call, its arguments and the return value to standard error output. To redirect this output to a file, use the -o command line option followed by the file name:
scl enable devtoolset-6 'strace -o file_name program [argument...]'
Replace file_name with the name of the file.
Example 8.1. Redirecting Output to a File
Consider a slightly modified version of the
fibonacci file from Example 7.1, “Compiling a C Program With Debugging Information”. This executable file displays the Fibonacci sequence and optionally allows you to specify how many members of this sequence to list. To run the strace utility on this file and redirect the trace output to fibonacci.log, type:
~]$ scl enable devtoolset-6 'strace -o fibonacci.log ./fibonacci 20'
1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 4181 6765
This creates a new plain-text file called
fibonacci.log in the current working directory.
8.2.2. Tracing Selected System Calls
To trace only a selected set of system calls, run the
strace utility with the -e command line option:
scl enable devtoolset-6 'strace -e expression program [argument...]'
Replace expression with a comma-separated list of system calls to trace or any of the keywords listed in Table 8.1, “Commonly Used Values of the -e Option”. For a detailed description of all available values, see the strace(1) manual page.
Table 8.1. Commonly Used Values of the -e Option
| Value | Description |
|---|---|
file | System calls that accept a file name as an argument. |
process | System calls that are related to process management. |
network | System calls that are related to networking. |
signal | System calls that are related to signal management. |
ipc | System calls that are related to inter-process communication (IPC). |
desc | System calls that are related to file descriptors. |
Example 8.2. Tracing Selected System Calls
Consider the
employee file from Example 10.1, “Using memstomp”. To run the strace utility on this executable file and trace only the mmap and munmap system calls, type:
~]$ scl enable devtoolset-6 'strace -e mmap,munmap ./employee'
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f896c744000
mmap(NULL, 61239, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f896c735000
mmap(0x3146a00000, 3745960, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x3146a00000
mmap(0x3146d89000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x189000) = 0x3146d89000
mmap(0x3146d8e000, 18600, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x3146d8e000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f896c734000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f896c733000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f896c732000
munmap(0x7f896c735000, 61239) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f896c743000
John,john@example.comDoe,
+++ exited with 0 +++8.2.3. Displaying Time Stamps
To prefix each line of the trace with the exact time of the day in hours, minutes, and seconds, run the
strace utility with the -t command line option:
scl enable devtoolset-6 'strace -t program [argument...]'
To also display milliseconds, supply the
-t option twice:
scl enable devtoolset-6 'strace -tt program [argument...]'
To prefix each line of the trace with the time required to execute the respective system call, use the
-r command line option:
scl enable devtoolset-6 'strace -r program [argument...]'Example 8.3. Displaying Time Stamps
Consider an executable file named
pwd. To run the strace utility on this file and include time stamps in the output, type:
~]$ scl enable devtoolset-6 'strace -tt pwd'
19:43:28.011815 execve("./pwd", ["./pwd"], [/* 36 vars */]) = 0
19:43:28.012128 brk(0) = 0xcd3000
19:43:28.012174 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fc869cb0000
19:43:28.012427 open("/etc/ld.so.cache", O_RDONLY) = 3
19:43:28.012446 fstat(3, {st_mode=S_IFREG|0644, st_size=61239, ...}) = 0
19:43:28.012464 mmap(NULL, 61239, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fc869ca1000
19:43:28.012483 close(3) = 0
...
19:43:28.013410 +++ exited with 0 +++8.2.4. Displaying a Summary
To display a summary of how much time was required to execute each system call, how many times were these system calls executed, and how many errors were encountered during their execution, run the
strace utility with the -c command line option:
scl enable devtoolset-6 'strace -c program [argument...]'Example 8.4. Displaying a Summary
Consider an executable file named
lsblk. To run the strace utility on this file and display a trace summary, type:
~]$ scl enable devtoolset-6 'strace -c lsblk > /dev/null'
% time seconds usecs/call calls errors syscall
------ ----------- ----------- --------- --------- ----------------
80.88 0.000055 1 106 16 open
19.12 0.000013 0 140 munmap
0.00 0.000000 0 148 read
0.00 0.000000 0 1 write
0.00 0.000000 0 258 close
0.00 0.000000 0 37 2 stat
...
------ ----------- ----------- --------- --------- ----------------
100.00 0.000068 1790 35 total
Where did the comment section go?
Red Hat's documentation publication system recently went through an upgrade to enable speedier, more mobile-friendly content. We decided to re-evaluate our commenting platform to ensure that it meets your expectations and serves as an optimal feedback mechanism. During this redesign, we invite your input on providing feedback on Red Hat documentation via the discussion platform.