Linux server thrashing using vmstat

You can use the vmstat command to detect thrashing of memory and hard disk as follows:

vmstat 2

where 2 represents the number of seconds to repeat.

You may see output similar to this

procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu-----
 r  b   swpd   free          buff      cache      si   so    bi    bo   in   cs us sy id wa st
 1  0   1600 2244636 193816 1154164    0    0     1     9    0    0  1  0 98  0  0
 1  0   1600 2244496 193816 1154184    0    0     0    46 1768 1432 26  1 73  0  0
 1  0   1600 2244496 193816 1154184    0    0     0     0 1756 1383 25  1 74  0  0
 1  0   1600 2244496 193816 1154184    0    0     0     0 1732 1318 26  0 74  0  0



The parameters of interest are si and so (swap in, swap out).
In this case a value of 0, means there is no thrashing

References:

http://www.linuxjournal.com/article/8178

Automated database backups

Automated Database Backups

Postgres

Assuming we are using Linux, create a file called .pgpass in the user’s home directory with the following details:

hostname:port:database:username:password

Then from the command-line run the following command:

pg_dump –U user dbname | gzip > ~/backup/db/$(date +%Y-%m-%d).psql.gz

Mysql

Assuming we are using Linux, create a file called ~/.my.cnf in the user’s home directory with the following details:

[mysqldump]

user=mysqluser

password=secret

Then from the command-line

mysqldump –u user dbname | gzip > ~/backup/db/$(date +%Y-%m-%d).psql.gz

Crontab

If the command is successful, then create and add this command to a script, for example runBackup.sh

Then schedule the job to run by editing your crontab:

crontab -e

For example, to run once a week on Saturday at 2AM:

0 2 * * 6 ~/runBackup.sh

 

References

http://stackoverflow.com/questions/2893954/how-to-pass-in-password-to-pg-dump

http://www.postgresql.org/docs/current/static/libpq-pgpass.html

http://stackoverflow.com/questions/9293042/mysqldump-without-the-password-prompt

Automated tomcat start up on server reboot

Automated start up on server reboot

Create a new tomcat user using the following command:

adduser tomcat

Create the following file /etc/init.d/tomcat:

#!/bin/bash

#

# tomcat       

#

# chkconfig:

# description: Start up the Tomcat servlet engine.

# Source function library.

. /etc/init.d/functions

RETVAL=$?

CATALINA_HOME="/usr/local/apache-tomcat-7.0.52"

case "$1" in

 start)

        if [ -f $CATALINA_HOME/bin/startup.sh ];

          then

            echo $"Starting Tomcat"

            /bin/su tomcat $CATALINA_HOME/bin/startup.sh

        fi

        ;;

 stop)

        if [ -f $CATALINA_HOME/bin/shutdown.sh ];

          then

            echo $"Stopping Tomcat"

            /bin/su tomcat $CATALINA_HOME/bin/shutdown.sh

        fi

        ;;

 *)

        echo $"Usage: $0 {start|stop}"

        exit 1

        ;;

esac

exit $RETVAL

Edit the file and change CATALINE_HOME to the location of where tomcat is found.

Grant execution write of the new file using the following command:

chmod 755 /etc/init.d/tomcat

Reassign the owner of the tomcat folder and all subfolders to the tomcat user:

chown tomcat:tomcat –R /usr/local/apache-tomcat-7.0.52

To start up on server reboot:

ln –s ../init.d/tomcat S71tomcat

 

Spring STS doesn't start up after many months of use

The problem:

After many months of using Spring STS IDE, I tried to reload the program but it always fails without any notifications or error messages. Even the "-clean" option failed to work.

When I insepected the log file found in the workspace/.metadata/log I noticed the following error:

 !ENTRY org.eclipse.core.jobs 2 2 2014-01-06 07:44:26.601  
 !MESSAGE Job found still running after platform shutdown. Jobs should be canceled by the plugin that scheduled them during shutdown: org.eclipse.core.internal.refresh.RefreshJob  
 !ENTRY org.eclipse.core.jobs 2 2 2014-01-06 07:44:26.601  
 !MESSAGE Job found still running after platform shutdown. Jobs should be canceled by the plugin that scheduled them during shutdown: org.eclipse.core.internal.refresh.RefreshJob  
 !ENTRY org.eclipse.ui 4 0 2014-01-06 07:44:26.602  
 !MESSAGE Error occurred during status handling  
 !STACK 0  
 java.lang.NullPointerException  
      at org.eclipse.ui.internal.statushandlers.StatusHandlerRegistry.<init>(StatusHandlerRegistry.java:61)  
      at org.eclipse.ui.internal.statushandlers.StatusHandlerRegistry.getDefault(StatusHandlerRegistry.java:91)  
      at org.eclipse.ui.statushandlers.StatusManager.getStatusHandler(StatusManager.java:135)  
      at org.eclipse.ui.statushandlers.StatusManager.handle(StatusManager.java:189)  
      at org.eclipse.ui.statushandlers.StatusManager.handle(StatusManager.java:231)  
      at org.eclipse.ui.statushandlers.StatusManager$StatusManagerLogListener.logging(StatusManager.java:305)  
      at org.eclipse.core.internal.runtime.RuntimeLog.logToListeners(RuntimeLog.java:160)  
      at org.eclipse.core.internal.runtime.PlatformLogWriter.logged(PlatformLogWriter.java:100)  
      at org.eclipse.equinox.log.internal.ExtendedLogReaderServiceFactory.safeLogged(ExtendedLogReaderServiceFactory.java:86)  
      at org.eclipse.equinox.log.internal.ExtendedLogReaderServiceFactory.logPrivileged(ExtendedLogReaderServiceFactory.java:205)  
      at org.eclipse.equinox.log.internal.ExtendedLogReaderServiceFactory.log(ExtendedLogReaderServiceFactory.java:178)  
      at org.eclipse.equinox.log.internal.ExtendedLogServiceFactory.log(ExtendedLogServiceFactory.java:65)  
      at org.eclipse.equinox.log.internal.ExtendedLogServiceImpl.log(ExtendedLogServiceImpl.java:87)  
      at org.eclipse.equinox.log.internal.LoggerImpl.log(LoggerImpl.java:54)  
      at org.eclipse.core.internal.runtime.PlatformLogWriter.logging(PlatformLogWriter.java:43)  
      at org.eclipse.core.internal.runtime.RuntimeLog.log(RuntimeLog.java:96)  
      at org.eclipse.core.internal.jobs.JobManager.doShutdown(JobManager.java:606)  
      at org.eclipse.core.internal.jobs.JobManager.shutdown(JobManager.java:252)  
      at org.eclipse.core.internal.jobs.JobActivator.stop(JobActivator.java:55)  
      at org.eclipse.osgi.framework.internal.core.BundleContextImpl$2.run(BundleContextImpl.java:771)  
      at java.security.AccessController.doPrivileged(Native Method)  
      at org.eclipse.osgi.framework.internal.core.BundleContextImpl.stop(BundleContextImpl.java:764)  
      at org.eclipse.osgi.framework.internal.core.BundleHost.stopWorker(BundleHost.java:510)  
      at org.eclipse.osgi.framework.internal.core.AbstractBundle.suspend(AbstractBundle.java:566)  
      at org.eclipse.osgi.framework.internal.core.Framework.suspendBundle(Framework.java:1206)  
      at org.eclipse.osgi.framework.internal.core.StartLevelManager.decFWSL(StartLevelManager.java:592)  
      at org.eclipse.osgi.framework.internal.core.StartLevelManager.doSetStartLevel(StartLevelManager.java:257)  
      at org.eclipse.osgi.framework.internal.core.StartLevelManager.shutdown(StartLevelManager.java:215)  
      at org.eclipse.osgi.framework.internal.core.InternalSystemBundle.suspend(InternalSystemBundle.java:284)  
      at org.eclipse.osgi.framework.internal.core.Framework.shutdown(Framework.java:692)  
      at org.eclipse.osgi.framework.internal.core.Framework.close(Framework.java:600)  
      at org.eclipse.core.runtime.adaptor.EclipseStarter.shutdown(EclipseStarter.java:400)  
      at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:200)  
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)  
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)  
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)  
      at java.lang.reflect.Method.invoke(Method.java:601)  
      at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:636)  
      at org.eclipse.equinox.launcher.Main.basicRun(Main.java:591)  
      at org.eclipse.equinox.launcher.Main.run(Main.java:1450)  
      at org.eclipse.equinox.launcher.Main.main(Main.java:1426)  

Solution

It appears that it may have gotten itself into a bad state. To reset this persisted state we can use the "-cleanPersistedState" option, when launching the application.


Reference: http://stackoverflow.com/questions/15372023/eclipse-will-not-start-and-i-havent-changed-anything

How to revoke access to tables prior to postgres 9.0

SELECT 'REVOKE SELECT ON TABLE ' || relname || ' FROM some_user;' FROM pg_class JOIN pg_namespace ON pg_namespace.oid = pg_class.relnamespace WHERE nspname = 'public';

Postgres grant read only

Prior to postgres 9.0 you can use this:

 SELECT 'GRANT SELECT ON ' || relname || ' TO xxx;'  a
 FROM pg_class JOIN pg_namespace ON pg_namespace.oid = pg_class.relnamespace  
 WHERE nspname = 'public' AND relkind IN ('r', 'v')  

Postgres 9+ you can use this:

 GRANT SELECT ON ALL TABLES IN SCHEMA public TO xxx;  

Reference:

http://stackoverflow.com/questions/760210/how-do-you-create-a-read-only-user-in-postgresql

Blocked loading mixed active content

Problem

With the latest versions of firefox, a javascript file fail to load from an external site such as google using the following code:

 <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jqueryui/1.10.3/jquery-ui.js"></script>  

The connection was secure running on HTTPS. However the connection to load the javascript file was not secure running purely on HTTP.

Solution

To get the javascript file to load properly I simply changed the SRC URL to use HTTPS as shown below:

 <script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jqueryui/1.10.3/jquery-ui.js"></script>