CST8177 - Linux II
midterm, system services, logs 
Todd Kelley 
kelleyt@algonquincollege.com 

CST8177- Todd Kelley 
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.quota command 

.system services 

.syslog 

.logger command line utility     


 
     

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Today's Topics





.individual users can check their individual quota 

."quota" command 

.block usage and limits 

.inode usage and limits 

.remainder on grace period if over soft limit 



 

Quota
CST8177 - Todd Kelley 

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.We've seen several system services by now 

.NTP service: keeps clock accurate 

.ntpd : the daemon 

./etc/ntp.conf : the daemon config file 

./etc/init.d/ntpd : the SysVinit script 

.ntpd daemon itself IS the client (of an ntp server) 

.ntpd logs to /var/log/messages  




System Services: examples
CST8177 - Todd Kelley 

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.SSH service: logins with Putty.exe or ssh 

.sshd : the daemon (SSH server) 

./etc/ssh/sshd_config : the daemon config file 

./etc/init.d/sshd : the SysVinit script 

.client program: putty.exe, ssh, scp, and more 

.daemon logs its messages to /var/log/secure 

.client manpage: man ssh 

.daemon manpage: man sshd 

.daemon config file manpage: man 5 sshd_config 

.client config file manpage: man 5 ssh_config 


.If we stop the sshd daemon, noone can log in over SSH  



System Services: examples
CST8177 - Todd Kelley 

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.daemon: 

.a program, launched at boot time usually 

./etc/init.d/* : the SysVinit scripts for starting, stopping, restarting, getting status of daemons 


.doesn't terminate - it keeps providing the service 

.many daemons, but not all, take requests from a corresponding client program 

.examples: 

.sshd : secure shell daemon, serves the ssh client 

.httpd : web server daemon, serves web browser client 

.crond : cron daemon, no client 

.ntpd: a client that provides a system service and uses an ntp server 





System Services: daemons
CST8177 - Todd Kelley 

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.System Service Daemons have config files 

.Normally maintained somewhere in /etc/ 

.Often end in ".conf" 

.Default config file comes with install package 

.System administrators customize them 

.Config files control various parameters 

.some parameters apply to many services: 

.how should logging be done 

.what port should the service listen on 


.some are specific to an individual service: 

.ntpd: which ntp server should be used 

.sshd: which version(s) of SSH protocol to use  





System Services: config files
CST8177 - Todd Kelley 

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.Often config files have many comments in them 

.# is a common comment character 

.usually lines beginning with # are ignored 


.Various possible options will be "commented out" 

.Those options can be activated by "uncommenting" them 



config files (cont'd)
CST8177 - Todd Kelley 

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.From /etc/ssh/sshd_config 


# Logging 
# obsoletes QuietMode and FascistLogging 
SyslogFacility AUTH 
#SyslogFacility AUTHPRIV 
#LogLevel INFO 
 
# Authentication: 
 
#LoginGraceTime 2m 
#PermitRootLogin yes 
#StrictModes yes 
#MaxAuthTries 6 
 

config files (cont'd)
CST8177 - Todd Kelley 

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To comment out this line 
SyslogFacility AUTH 
it becomes 
#SyslogFacility AUTH 
 
and to uncomment this line 
#SyslogFacility AUTHPRIV 
it becomes  
SyslogFacility AUTHPRIV 
 

config files (cont'd)
CST8177 - Todd Kelley 

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.So far in your work with computers you've seen more of the clients than the servers. 

.Examples of clients you use all the time 

.ssh, putty.exe 

.Web Browser 

.Explorer (Windows Networking) 

.ftp 

.DHCP (example: network connection at Algonquin) 


.Each of these clients requires a server to be running at the "other end" 



System Services: clients
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.Daemons need a place where they can send their output 

.Most daemons use the syslog logging service 

.Centralized logs are easier to manage 

.syslog is itself a daemon 

.daemon : syslogd 

.config file : syslog.conf 

.client program: logger command line utility, as well as all the other daemons 


.daemons send their messages to syslog, and syslog puts those messages in an appropriate place, usually a file under /var/log/ 



System Services: logging
CST8177 - Todd Kelley 

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.Contents of /etc/syslog.conf is a set of rules  

.Every rule consists of two fields:  


selector                    action  
 
.Every selector has two parts: 


facility.priority 

Syslog config: /etc/syslog.conf
CST8177 - Todd Kelley 

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.auth : authorization 

.authpriv : private authorization 

.cron : crond 

.daemon : other misc daemons 

.kern : the kernel 

.lpr : printer 

.mail : email 

.news : usenet news 

.syslog : syslog itself 

.user : user messages 

.uucp : unix to unix copy 

.local0 through local7 : local use 

.* : all of the above  




Syslog Facilities
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.In order of increasing priority: 

.debug : debug level messages 

.info : normal information 

.notice : normal but significant, unusual 

.warning : not an error, but action should be taken 

.err : error condition, non-urgent failure 

.crit : critical condition, failure in primary system 

.alert : action needed immediately 

.emerg : panic, system unusable, notify all 

.* : all of the above 

.none: none of the above for the given facility 




Syslog Priorities
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.Absolute pathname of a file 

.put the message (log entry) in that file 

.dash in front means omit syncing on every entry 


.Terminal or Console : ex /dev/console 

.write the message on that screen 


.@hostname : remote machine 

.send the message to syslog on the remote machine 


.username 

. write the message on that user's terminal 


.* : everyone logged in 

.write the message on everyone's screen 


.named pipe (fifo) : useful for debugging 



Syslog actions
CST8177 - Todd Kelley 

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