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Title
How to use "strace" or "s trace" on Linux -
Description
You can generate Linux debugging files for process issues using "STRACE"
STRACE is a diagnostic, debugging and instructional user space utility for Linux. It is used to monitor interactions between processes and the Linux kernel, which include system calls, signal deliveries, and changes of process state. -
Cause
The most common usage is to start a program using strace, which prints a list of system calls made by the program.
This is useful if the program continually crashes, or does not behave as expected; for example using strace may reveal that the program is attempting to access a file which does not exist or cannot be read.
This proves to be useful if the NetVault process fails when starting up, in some cases it is able to run for a few seconds before the service goes down.
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Resolution
Enabling strace on a NetVault process
- Open a SSH connection to the server where Netvault is running
- Obtain the process Id for the Netvault process using the next command
[root@server ~]# ps -ef |grep nvroot 11077 31412 0 07:57 pts/1 00:00:00 grep nv3. Add the Process ID to the next command and create a file to send the debugging files to that file[root@server ~]# strace -p 15243 -o strace-test.txtProcess 15243 attached4. Access from another SSH connection on the server to see the debugging files that are being generated.[root@sap ~]# tail -f strace-test.txtwait4(-1, 0x7fff12c76d9c, WNOHANG|WSTOPPED, NULL) = 0select(0, NULL, NULL, NULL, {1, 0}) = 0 (Timeout)wait4(-1, 0x7fff12c76d9c, WNOHANG|WSTOPPED, NULL) = 0select(0, NULL, NULL, NULL, {1, 0}) = 0 (Timeout)wait4(-1, 0x7fff12c76d9c, WNOHANG|WSTOPPED, NULL) = 0select(0, NULL, NULL, NULL, {1, 0}) = 0 (Timeout)wait4(-1, 0x7fff12c76d9c, WNOHANG|WSTOPPED, NULL) = 0select(0, NULL, NULL, NULL, {1, 0}) = 0 (Timeout)wait4(-1, 0x7fff12c76d9c, WNOHANG|WSTOPPED, NULL) = 0select(0, NULL, NULL, NULL, {1, 0}) = 0 (Timeout)wait4(-1, 0x7fff12c76d9c, WNOHANG|WSTOPPED, NULL) = 0select(0, NULL, NULL, NULL, {1, 0}^CTo exit, use CTRL-C
*The above example shows that the process being stopped, likely due to another process. It may be required to reboot the system, or verify if there are any other NetVault processes running that are preventing the NetVault process from starting.