quartz/content/notes/10-scheduled-tasks-and-logs.md

title	tags
10-scheduled-tasks-and-logs	lecture cosc301

DAEMON

• A process that runs in the background and is independent of control from all terminals
• Reasons for daemons’ independence of terminals
  • Prevent daemons’ error message from appearing on a user’s terminal
  • Signals generated from terminal keys must not affect any daemons that were started from that terminal earlier
• Typical daemons
  • crond, syslogd

DAEMONIZATION

if( (pid = fork()) != 0) exit(0); //parent terminates 
setsid(); // become session leader 
signal(SIGHUP, SIG_IGN); if( (pid = fork()) != 0) exit(0); //new child continues 
//now it becomes daemon

The purpose is to make the process independent of the control from any terminals.

[!INFO] when you are independent from parent you are a leader. need to ignore sighup signal otherwise child would be automatically terminated when the parent is killed.

SCHEDULED TASKS

• Automating tasks
  • crond and crontab
  • crond is a very important daemon for automatically executing tasks
  • Tasks can be configured to repeat hourly, daily, weekly,…, or even per minute.
• Possible uses
  • Clean file systems
  • Log rotate
  • Check log files
  • Monitor system status and resources

[!INFO] can run any command/script on a schedule for security you should scan logs everyday to check for keywords useing grep, sed, awk

SYSLOGD

• How it works?
  • Read the configuration file /etc/syslog.conf
  • A Unix domain socket is created and bound to the pathname /var/run/log
  • A UDP socket is created and bound to port 514
  • Runs in an infinite loop that calls select, waiting for any one of the above descriptors to be readable, reads the log message, and does what the configuration file says to do with that message.
  • If the daemon receives the SIGHUP signal, it rereads the configuration file

[!INFO] syslogd is a daemon.

LOGGING FUNCTIONS

• How start and close logging?
  • Create a Unix domain datagram socket and send out messages to the pathname the daemon has bound, or send them to port 514 by a UDP socket
  • openlog() and closelog()
• How to send log messages
  • void syslog(int priority, const char *message, …);
  • priority is a combination of a level and a facility shown later
  • message is like a format string to printf, with the addition of a %m specification, which is replaced with the error message corresponding to the current value of errno.

[!INFO] some log messages go to other locations

Example code

• openlog ("mylibrary", option, priority);
• syslog (LOG_INFO, “My library has been invoked”);
• closelog ();

Level

• LOG_EMERG (0): system is unusable
• LOG_ALERT (1): action must be taken immediately
• LOG_CRIT (2): critical conditions
• LOG_ERR (3): error conditions
• LOG_WARNING (4): warning conditions
• LOG_NOTICE (5): normal but significant conditions
• LOG_INFO (6): informational
• LOG_DEBUG (7): debug-level messages, has lowest priority

Facility

• Identify the type of process sending the message
• Facilities
  • LOG_AUTH: security/authorization messages
  • LOG_AUTHPRIV: security/authorization messages (private)
  • LOG_CRON: from crond
  • LOG_KERN: kernel messages
  • LOG_MAIL: mail system
  • LOG_USER: random user-level messages (default)
  • LOG_FTP: from ftpd
  • LOG_LPR: line printer system
  • LOG_SYSLOG: internal messages from syslogd
  • LOG_LOCAL0
  • LOG_LOCAL7: local, discretional use by programmers.

klogd

• klogd provides a facility for system admin to check only kernel messages (which can also be checked through syslogd)
• Kernel messages can be read from /proc/kmsg
• Use /proc/sys/kernel/printk to control the level of log messages.
  • cat /proc/sys/kernel/printk