I had a program that was segfaulting.
When I went to investigate and ran dmesg I could see lines like this:
[955.915050] traps: foo_bar[123] general protection ip:7f5fcc2d4306 sp:7ffd9e5868b8 ...
Now the program has been fixed and I'm trying to write some analysis scripts across different systems to find similar messages and was hoping to induce a line in the dmesg log to get a baseline for what to look for and see if there's a difference between, say, a sigbus(10) and a sigill(4)
I tried to do it via kill -11 on the command line . No entry in dmesg
I tried to do it via signal(getpid(), 11) in the code. No entry in dmesg
I tried to do it via signal 11 after attaching in gdb . No entry in dmesg
I tried to do it via writing bad code and it worked for SEGV, but I can't figure out how to trigger a SIGBUS (for example)
I'm guessing that there is more than one path for handling the signal depending on how it occurs and my attempts above just aren't doing it the right way.
How can I trigger/send a signal to my program that'll get a line in dmesg? Is there some kernel or log configuration I can twiddle to get those lines?
Update:
" __builtin_trap: when to use it? " shows how to get a SIGILL but alas doesn't have a signal-agnostic solution)
Ok so I am having problems with syslog on Raspbian Stretch. I am trying to write to /var/log/blah.log using local0 as my facility. I am using gnu C++ 11 As the application is being written in C++ so I trying to create a logging class.
My /etc/syslog.conf has the following entry
local0.* /var/log/blah.log
... and I have restarted the service and the Pi.
My code to open the log is as follows:
setlogmask(LOG_UPTO(LOG_DEBUG));
openlog(blah, LOG_PERROR | LOG_CONS | LOG_NDELAY, LOG_LOCAL0);
...and my logging code is:
syslog(LOG_INFO | LOG_LOCAL0, fullMessage.c_str());
There is no /var/log/blah.log file created and no log entries written, although the message is written to the console as I am using LOG_CONS.
If I replace LOG_LOCAL0 with LOG_USER I am successfully able write to user.log.
I do want to be able to write to the custom log file because:
a) it is easy to ask a user to look at that file for debugging purposes
b) it should work!!
As I have stated I have looked through the numerous posts on this site and others and still cannot get it top work so posting links to man pages and other articles won't help!
Currently I am tring to write a program to monitor Tuxedo. from the official documents, I found MIB is suitable for writting program to monitor it. I have read a quite lot of document of here http://docs.oracle.com/cd/E13203_01/tuxedo/tux90/rf5/rf5.htm#998207. Although there are so many instructions of very class, there is no any guide to tell me how to use it from the beginning. I have tried to search on github however unfortuanately there is no any code relating to tuxedo mib. Does any one have some good sample code?
Thanks a lot.
Here a Shell-function that reads the blocktime from Tuxedo:
get_blocktime() {
TmpErr=/tmp/ud32err_$$
rtc=0
ud32 -Ctpsysadm <<EOF 2>$TmpErr | grep TA_BLOCKTIME | cut -f2
SRVCNM .TMIB
TA_CLASS T_DOMAIN
TA_OPERATION GET
EOF
# ud32 has no good error-handling
if [ -s $TmpErr ]; then
echo "$PRG: Error calling ud32:"
cat $TmpErr 1>&2
rtc=1
fi
rm $TmpErr
exit $rtc
}
There are several examples of accessing MIB with Python https://github.com/PacktPublishing/Modernizing-Oracle-Tuxedo-Applications-with-Python/tree/main/Chapter06. For example:
import tuxedo as t
t.tpinit(cltname="tpsysop")
machine = t.tpadmcall(
{
"TA_CLASS": "T_MACHINE",
"TA_OPERATION": "GET",
"TA_FLAGS": t.MIB_LOCAL,
}
).data
A couple of notes:
you will need the TA_FLAGS set to MIB_LOCAL to return statistics (not done by default)
you might want to use tpadmcall() function instead of calling the .TMIB service. The function is much lighter on the system and does not increase Tuxedo statistics (number of service calls). The main limitation of tpadmcall is the limited size of the response so you will need to call the .TMIB service for server and queue statistics if your application has tens of them.
If the code example is not enough, you can check the chapter 6 of the book Modernizing Oracle Tuxedo Applications with Python.
I have some C code for calling .TMIB to monitor Tuxedo application here: https://github.com/TuxSQL/tuxmon
That should get you started.
I wrote a simple test application to log something in a log file. I am using linux mint and after the application executes I try to view the log using this command:
tail -n 100 /var/log/messages
but the file messages does not exist neither tested or something. Below you can find my code. Maybe I am doing something wrong, the file isn't stored there or I need to enable logging in linux mint.
#include <stdio.h>
#include <stdlib.h>
#include <syslog.h>
void init_log()
{
setlogmask(LOG_UPTO(LOG_NOTICE));
openlog("testd",LOG_CONS | LOG_PID | LOG_NDELAY, LOG_LOCAL1);
}
int main(void) {
init_log();
printf("Session started!");
syslog(LOG_NOTICE, "Session started!!");
closelog();
return EXIT_SUCCESS;
}
On my Ubuntu machine, I can see the output at /var/log/syslog.
On a RHEL/CentOS machine, the output is found in /var/log/messages.
This is controlled by the rsyslog service, so if this is disabled for some reason you may need to start it with systemctl start rsyslog.
As noted by others, your syslog() output would be logged by the /var/log/syslog file.
You can see system, user, and other logs at /var/log.
For more details: here's an interesting link.
Default log location (rhel) are
General messages:
/var/log/messages
Authentication messages:
/var/log/secure
Mail events:
/var/log/maillog
Check your /etc/syslog.conf or /etc/syslog-ng.conf (it depends on which of syslog facility you have installed)
Example:
$ cat /etc/syslog.conf
# Log anything (except mail) of level info or higher.
# Don't log private authentication messages!
*.info;mail.none;authpriv.none /var/log/messages
# The authpriv file has restricted access.
authpriv.* /var/log/secure
# Log all the mail messages in one place.
mail.* /var/log/maillog
#For a start, use this simplified approach.
*.* /var/log/messages
In addition to the accepted answer, it is useful to know the following ...
Each of those functions should have manual pages associated with them.
If you run man -k syslog (a keyword search of man pages) you will get a list of man pages that refer to, or are about syslog
$ man -k syslog
logger (1) - a shell command interface to the syslog(3) system l...
rsyslog.conf (5) - rsyslogd(8) configuration file
rsyslogd (8) - reliable and extended syslogd
syslog (2) - read and/or clear kernel message ring buffer; set c...
syslog (3) - send messages to the system logger
vsyslog (3) - send messages to the system logger
You need to understand the manual sections in order to delve further.
Here's an excerpt from the man page for man, that explains man page sections :
The table below shows the section numbers of the manual followed by
the types of pages they contain.
1 Executable programs or shell commands
2 System calls (functions provided by the kernel)
3 Library calls (functions within program libraries)
4 Special files (usually found in /dev)
5 File formats and conventions eg /etc/passwd
6 Games
7 Miscellaneous (including macro packages and conven‐
tions), e.g. man(7), groff(7)
8 System administration commands (usually only for root)
9 Kernel routines [Non standard]
To read the above run
$man man
So, if you run man 3 syslog you get a full manual page for the syslog function that you called in your code.
SYSLOG(3) Linux Programmer's Manual SYSLOG(3)
NAME
closelog, openlog, syslog, vsyslog - send messages to the system
logger
SYNOPSIS
#include <syslog.h>
void openlog(const char *ident, int option, int facility);
void syslog(int priority, const char *format, ...);
void closelog(void);
#include <stdarg.h>
void vsyslog(int priority, const char *format, va_list ap);
Not a direct answer but hopefully you will find this useful.
You have to tell the system what information to log and where to put the info. Logging is configured in the /etc/rsyslog.conf file, then restart rsyslog to load the new config. The default logging rules are usually in a /etc/rsyslog.d/50-default.conf file.
syslog() generates a log message, which will be distributed by syslogd.
The file to configure syslogd is /etc/syslog.conf.
This file will tell your where the messages are logged.
How to change options in this file ?
Here you go
http://www.bo.infn.it/alice/alice-doc/mll-doc/duix/admgde/node74.html
Logging is very configurable in Linux, and you might want to look into your /etc/syslog.conf (or perhaps under /etc/rsyslog.d/). Details depend upon the logging subsystem, and the distribution.
Look also into files under /var/log/ (and perhaps run dmesg for kernel logs).
I'm running Ubuntu under WSL(Windows Subsystem for Linux) and systemctl start rsyslog didn't work for me.
So what I did is this:
$ service rsyslog start
Now syslog file will appear at /var/log/
How can I, in C, output a value from a syscall to the Linux console so that it will be visible after a dmesg? What method do I use for printing?
You're looking for the printk() function; some documentation on the types that it supports is found in Documentation/printk-formats.txt. It is defined in kernel/printk.c.
I assume you mean in the user-space. You can write the string to /dev/kmsg. In shell, just echo it. In C, it would be also very easy.
[root#cr0 ~]# echo hello > /dev/kmsg
[root#cr0 ~]# dmesg | tail -1
[24156.408735] hello
But if you mean in kernel space, of course, you need to call printk().
In addition, you might be interested (even if that does not answer exactly your question), by the openlog & syslog functions. From within an application, they are the proper way to get system logging.