Gnanam's questions

I'm not a good Shell Script expert. Can somebody help me to understand and explain the statement [ ! -z ${TRUE:-} ] && [ ${TRUE:-} == 'true' ] &&from the following snippet. What is this specific statement doing and/or being validated for?

However, am able to understand this statement: TRUE=$($JBOSS_TWIDDLE get jboss.system:type=Server Started |grep Started |cut -d"=" -f2). This basically calling a JBoss's JMX command-line tool to check the server start status.

Code Snippet:

while [ $i -lt 180 ]; do
        TRUE=$($JBOSS_TWIDDLE get jboss.system:type=Server Started |grep  Started |cut -d"=" -f2)

        [ ! -z ${TRUE:-} ] && [ ${TRUE:-} == 'true' ] && {
    echo "The $JBOSS_NAME server is up and running."
    return
}

I've seen so many examples/usages about how to display/hide line numbers in vi edit mode.

To turn on line numbers: Type :set number in edit mode

To turn off line numbers: Type :set nonumber in edit mode

I wonder whether there is any convenient way/option available (that I may not be knowing) to specify/mention this option at the time of opening the file from the command line?

NOTE: For example, to go to a specific line inside a file after opening it, we can conveniently say vi +/<linenumber> <filename> from the command line.

We're at the juncture (I can even say, right time) that we need to separate our database server apart from our application web server. This we arrived at after careful & thorough monitoring of the server (load average, CPU usage, etc.) itself.

When the database server is separated:

1. What would be the ideal setup/best practice for network communication path between 2 servers? If it were running on the same server, connectivity between database and application would make use of TCP/IP communication, but how it should be running/setup when it is separated, so that performance is not majorly affected? For example, currently our JDBC URL looks like jdbc:postgresql://localhost:9999/ourproductiondb, probably this localhost would be changed to private IP address of the database server.

2. In our application, we also allow application users to submit/attach attachments (.txt, .doc, .pdf, .xls, etc.), which are actually stored physically in server disk and only its file path is stored in the database. Which is the ideal place/approach for maintaining/keeping documents physically, either in application web server or in database server?

We're very new into this area of separating database as a separate server and our knowledge on this is very limited. Therefore, any resources, links, documentation, articles, guidelines, suggestion etc. in this regard are highly welcome and really appreciated.

NOTE: Our tools of trade are: RHEL5 64-bit, Apache Tomcat 6.0.10, JDK 1.6, PostgreSQL 8.2.22, pgpool 2.0.1

I'm looking for a single command to list all files recursively from a given directory along with its modified time. It would also be nice if it can produce output in a tree-like format as produced by tree command.

NOTE: I'm running Red Hat Enterprise Linux Server release 5.

EDIT: The option -D of tree command prints only the date part of the last modification time for past years, though it display date with time for current year. Here, in this case, I'm expecting to print date with time for past years as well.

Background of our setup:
We've hosted our web-based application in Amazon EC2 US East (Virginia) Region. Our instance is based on Linux distribution (CentOS) and AMI is S3-backed. 1 EBS volume (400 GB size) is attached to this instance.

Question:
We've planned to migrate our deployment to US West (N. California) Region. From AWS doc, I understood that for moving AMI, there is a command-line tool available - ec2-migrate-bundle. But for moving EBS volume across Region, currently there is no tool available.

I'm looking for easiest and/or fastest way of copying/moving EBS volume from one Region to another. Also, are there any hidden risks involved during and/or after the migration?

Experts ideas/suggestions/recommendations on this are highly appreciated.

Our production server is running Apache v2.2.4 on CentOS5.2. Mono v1.2.4 is integrated within Apache.

Recently, we faced a problem in our production server. From Apache's access_log, I found a HTTP 500 internal server error for one of the HTTP request and all subsequent HTTP requests also failed but with HTTP 503 service unavailable error. From thereafter, none of the requests were successful. Also, only later some time, we realized that our application was not working because of this error and then we restarted Apache service.

My questions are,

1. in this kind of situation, how do I automatically restart Apache service when HTTP 503 error is encountered? Is there any Apache directive available to set?
2. in general, what would cause a HTTP 503 error in Apache?

NOTE: Mono helps in running applications developed in .NET on a Linux-based OS.

EDIT: I agree on finding the root cause of this problem. In fact, we've been analyzing that too. Till we resolve it, am finding whether this could be restarted immediately on its own without having any downtime/service disruption for application users.

Having only remote access (no physical access), to a server (that is SSH), how do I (or may be is it possible):

1. find out whether it is RAID configured or not? If it is RAID configured, whether it is software or hardware RAID? What level of RAID it is?
2. find the RPM speed of the hard disk?

NOTE: In this case, I've access to both RHEL4/5 and CentOS4/5 based Linux servers.

EDIT

Here is an output of mount command from a RHEL4 server:

/dev/mapper/VolGroup00-LogVol00 on / type ext3 (rw)
none on /proc type proc (rw)
none on /sys type sysfs (rw)
none on /dev/pts type devpts (rw,gid=5,mode=620)
usbfs on /proc/bus/usb type usbfs (rw)
/dev/sda1 on /boot type ext3 (rw)
none on /dev/shm type tmpfs (rw)
none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw)
sunrpc on /var/lib/nfs/rpc_pipefs type rpc_pipefs (rw)

How do I dynamically check/list a particular Apache configuration directive? I know that this can be checked manually from httpd.conf file, but is there any other way this can be confirmed/found from a running Apache server process?

For example: In my case, I was checking for KeepAlive configuration directive. I even checked with the command /usr/local/apache2/bin/apachectl -h, but I don't find it here.

Our production server is running CentOS5 64-bit arch.

Because there are no RPM available currently for SQLite latest version (v3.7.3), I created RPM using rpmbuild the very first time by following the instructions given here. I was able to successfully create RPM for 64-bit (x86_64) architecture. But am not able to create RPM for 32-bit (i386) architecture. It failed with the following errors:

...
...
...
+ ./configure --build=x86_64-redhat-linux-gnu --host=x86_64-redhat-linux-gnu --target=i386-redhat-linux-gnu --program-prefix= --prefix=/usr --exec-prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc --datadir=/usr/share --includedir=/usr/include --libdir=/usr/lib64 --libexecdir=/usr/libexec --localstatedir=/var --sharedstatedir=/usr/com --mandir=/usr/share/man --infodir=/usr/share/info --enable-threadsafe
checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
checking for gawk... gawk
checking whether make sets $(MAKE)... yes
checking for style of include used by make... GNU
checking for x86_64-redhat-linux-gnu-gcc... no
checking for gcc... gcc
checking for C compiler default output file name... 
configure: error: C compiler cannot create executables
See `config.log' for more details.
error: Bad exit status from /var/tmp/rpm-tmp.73141 (%build)


RPM build errors:
    Bad exit status from /var/tmp/rpm-tmp.73141 (%build)

This is the command I called: rpmbuild --target i386 -ba sqlite.spec

My question is, how do I create RPM for 32-bit arch from a 64-bit arch server?

Our production server is running sqlite-3.3.6-2 on CentOS release 5.2 (Final).

We're planning to upgrade SQLite to the latest v3.7.3 (atleast v3.5+). But there is no RPM available in SQLite website and not able to find one from google search also.

But I'm finding v3.5+ RPM for RHEL3 here. Since we're running CentOS5 64-bit,

1. Is it OK to install a RHEL3 64-bit RPM package on a CentOS5 64-bit server?
2. In case, if it can be installed, will there be any implications/side-effects?

In general, can we install a RPM built for lower version of OS (ex: RHEL3) on a higher version of OS (ex: RHEL5)?

Our production server is running CentOS release 5.2 (Final).

How do I see/get/list all the dependencies of an already installed RPM package?

For example: SQLite v3.3.6 is already installed in the server. I want to see all the dependencies of this particular package.

Here is the output of the command: rpm -qa |grep sqlite

python-sqlite-1.1.7-1.2.1
sqlite-3.3.6-2
sqlite-3.3.6-2

Also, why it is listing 2 entries of sqlite-3.3.6-2 here?

My server is CentOS release 5.2 (Final).

How do I uninstall an application which was installed from a Linux Installer, that is extension of type .bin?

For example: I installed an application called Mono using Linux Installer and now I want to uninstall this application.

If it's a RPM installation, we can use 'rpm -e' and if it's installed from source we can use 'make uninstall'. Similarly, what is the equivalent way of uninstalling an application installed from a Linux Installer (.bin)?

NOTE: Mono is a cross platform, open source .NET development framework

I'm using the following Amazon EC2 resources in the US East (Virginia) region:

1. 1 Running Instance
2. 1 Elastic IP
3. 2 EBS Volumes
4. 100 EBS Snapshots
5. 1 Key Pair
6. 2 Security Groups
7. 5 My Own AMIs (customized based on my application stack)

My instance is based on Linux distribution (CentOS) and my AMIs are S3-backed. Both EBS volumes are mounted on this running instance.

We're planning to migrate our deployment to US-West region. Because Amazon EC2 resources are not shared across regions, my questions are:

1. What are all the factors that I need to consider in advance?
2. What are all the recommended & different ways of migrating each EC2 resources from one region to the other?
3. Are there any hidden risks involved during and/or after the migration?

Experts ideas/suggestions/recommendations on this are highly appreciated.

Amazon has recently announced Micro instances for Amazon EC2. I'm also keep reading about "... allow you to burst CPU capacity when additional cycles are available."

My question is, what does CPU burst mean? I want to know/understand this better.

Any pointers, articles, documentation, etc. on the same are appreciated.

My OS is RHEL5.

I want to direct the console output produced by the following database command to a log/file.

psql mydb mydbuser -c "VACUUM ANALYZE VERBOSE"

I've tried out the following commands and is not working as expected. But it is printing output to the terminal console instead.

psql mydb mydbuser -c "VACUUM ANALYZE VERBOSE" > vacuum.log
psql mydb mydbuser -c "VACUUM ANALYZE VERBOSE" | tee vacuum.log

Here, in this case, is not the output produced by this command a standard input/output/error?

NOTE: psql is a terminal-based front-end to PostgreSQL. It enables you to type in queries interactively, issue them to PostgreSQL, and see the query results.

As the question is clear from the title, how do I change Linux services startup/boot order?

Using wget command, how do I allow/instruct to overwrite my local file everytime, irrespective of how many times I invoke.

Let's say, I want to download a file from the location: http://server/folder/file1.html

Here, whenever I say wget http://server/folder/file1.html, I want this file1.html to be overwritten in my local system irrespective of the time it is changed, already downloaded, etc. My intention/use case here is that when I call wget, I'm very sure that I want to replace/overwrite the existing file.

I've tried out the following options, but each option is intended/meant for some other purpose.

1. -nc => --no-clobber
2. -N => Turn on time-stamping
3. -r => Turn on recursive retrieving

Possible Duplicate:
Don’t understand [0:0] iptable syntax

My server is Red Hat Enterprise Linux Server release 5.

I'm not an expert in Linux iptables firewall. I've the following entries in iptables:

[root@myserver ~]# more /etc/sysconfig/iptables
# Generated by iptables-save v1.3.5 on Mon Sep 14 20:04:30 2009
*nat
:PREROUTING ACCEPT [10934:1556118]
:POSTROUTING ACCEPT [0:0]
:OUTPUT ACCEPT [111392:6686084]
-A PREROUTING -p tcp -m tcp --dport 80 -j REDIRECT --to-ports 5050
-A POSTROUTING -j MASQUERADE
-A OUTPUT -d 192.168.0.200 -p tcp -m tcp --dport 80 -j DNAT --to-destination 192.168.0.200:5050
-A OUTPUT -d 127.0.0.1 -p tcp -m tcp --dport 80 -j DNAT --to-destination 127.0.0.1:5050
COMMIT
# Completed on Mon Sep 14 20:04:30 2009

What does the value range in the bracket mean? For example, here: PREROUTING ACCEPT [10934:1556118], what does the range 10934:1556118 mean?

My server is Red Hat Enterprise Linux Server release 5.

I'm not an expert in Linux iptables firewall.

After installation, I find the following entries in /etc/sysconfig/iptables.

*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
-A INPUT -j ACCEPT
-A FORWARD -j ACCEPT
-A OUTPUT -j ACCEPT
COMMIT

What does this iptable filter restriction rule mean?

I've a Java standalone program scheduled to run as cron at every 10 minutes

I want to catch/write errors thrown by this Java program both in the log file and also as a separate error file (MyJavaStandalone.err).

I know the following commands:
Errors redirected to a separate file but not to log file

/usr/java/jdk1.6.0/bin/java MyJavaStandalone >> MyJavaStandalone.log 2>> MyJavaStandalone.err &

Both log and errors are redirected to the same log file, but errors alone are not written to a separate error file

/usr/java/jdk1.6.0/bin/java MyJavaStandalone >> MyJavaStandalone.log 2>&1 &