Category Archives: Linux

Install and setup CentOS7

After making a CentOS 7 minimal install and boot up for the first time. Here are, in my view, the tools and “must do” things that you will meed for day to day work.

Remove Intel Wifi devices firmware (do this only if you don’t use it):

yum remove iwl*

Update CentOS to the latest packages:

yum -y update

Install the tools:

yum install net-tools bind-utils wget vim

If you are in a vmware virtual machine install the virtualization tools:

yum install open-vm-tools

If you need, setup network

systemctl restart network.service

Setup aliases, so that messages from services can be sent to the correct email account:

vim /etc/aliases

Change the root: to the correct email account

# Person who should get root's mail
root: your@email

Then issue the fallowing command so that linux uses the new email account:


Next setup postfix to send email thru a valid mail server

vim /etc/postfix/

Using TLS

relayhost = your.mail.server:587

Without TLS

relayhost = your.mail.server

Finaly restart postfix

systemctl restart postfix.service

If you want you can install logwatch

yum install logwatch

The configure it to send you system logs emails

echo "MailTo = [email protected]" >> /etc/logwatch/conf/logwatch.conf

Instalar as vmware tools via rpm

O vmware é um dos sistemas de virtualização mais utilizados a nível profissional.

Ao instalar um vm CentOS 6.x no vmware é necessário instalar um conjunto de drivers para que o SO funcione de forma integrada com o hipervisor. Essas ferramentas chamam-se vmware-tools.
Para instalar as vmware-tools via rpm é necessário realizar os seguintes passos:

Instalar/criar o repositório da vmware:

echo '[vmware-tools]' > /etc/yum.repos.d/vmware.repo
echo 'name=VMware Tools' >> /etc/yum.repos.d/vmware.repo
echo 'baseurl=$basearch' >> /etc/yum.repos.d/vmware.repo
echo 'enabled=1' >> /etc/yum.repos.d/vmware.repo
echo 'gpgcheck=1' >> /etc/yum.repos.d/vmware.repo

Instalar a chave da vmware:

rpm --import ''

Executar o comando para instalar as vmware-tools:

yum -y install vmware-tools-esx-nox

ou, caso tenha o modo gráfico instalado:

yum -y install vmware-tools-esx

Send email from Linux command line

Every once a while you need to send email from a Linux command line and there you go to google try to find it…

With attachment:

echo "message" | mailx -s "subject" -a attachment email@dress
echo "message" | mutt -s "subject" -a attachment -- email@dress

Without attachment:

echo "message" | mail -s "subject" email@ddress

Postfix by default restrict attachment size to approx 10MB i.e. 10240000 bytes.

You can check it using following command:

postconf | grep message_size_limit

To change attachment-size to say 50 MB, run a command like:

postconf -e message_size_limit=52428800

Dell PowerEdge 1750 kernel panic on CentOS 6.x workaround

If you have an old Dell PowerEdge 1750 and want to install CentOS 6.x on it so that you can do something useful with it you will bump into kernel panic once you install it. So after some googling I’ve found this workaround to solve the kernel panic problem.


If somewhere on that list of line you find the folowing:

scb2_flash: warning - can't reserve rom window, continuing
resource map sanity check conflict: 0xfff00000 0xffffffff 0xfff80000 0xffffffff reserved
------------[ cut here ]------------
WARNING: at arch/x86/mm/ioremap.c:98 __ioremap_caller+0x435/0x450() (Not tainted)
Hardware name: PowerEdge 1750
Info: mapping multiple BARs. Your kernel is fine.
Modules linked in: scb2_flash(+) ext4 jbd2 mbcache sd_mod crc_t10dif sr_mod cdrom megaraid_mbox megaraid_mm ata_generic pata_acpi pata_serverworks dm_mirror dm_region_hash dm_log dm_mod [last unloaded: scsi_wait_scan]
Pid: 452, comm: modprobe Not tainted 2.6.32-431.5.1.el6.i686 #1
Call Trace:
 [] ? warn_slowpath_common+0x81/0xc0
 [] ? __ioremap_caller+0x435/0x450
 [] ? __ioremap_caller+0x435/0x450
 [] ? warn_slowpath_fmt+0x33/0x40
 [] ? __ioremap_caller+0x435/0x450
 [] ? scb2_flash_probe+0x99/0x2a0 [scb2_flash]
 [] ? ioremap_nocache+0x18/0x20
 [] ? scb2_flash_probe+0x99/0x2a0 [scb2_flash]
 [] ? scb2_flash_probe+0x99/0x2a0 [scb2_flash]
 [] ? local_pci_probe+0xb/0x10
 [] ? pci_device_probe+0x61/0x80
 [] ? driver_probe_device+0x87/0x290
 [] ? pci_match_device+0x12/0xa0
 [] ? __driver_attach+0x79/0x80
 [] ? __driver_attach+0x0/0x80
 [] ? bus_for_each_dev+0x52/0x80
 [] ? driver_attach+0x16/0x20
 [] ? __driver_attach+0x0/0x80
 [] ? bus_add_driver+0x1b7/0x2b0
 [] ? pci_device_remove+0x0/0x40
 [] ? driver_register+0x5f/0x110
 [] ? tracepoint_module_notify+0x1f/0x30
 [] ? scb2_flash_init+0x0/0x14 [scb2_flash]
 [] ? __pci_register_driver+0x3d/0xb0
 [] ? do_one_initcall+0x2f/0x1c0
 [] ? sys_init_module+0xb4/0x220
 [] ? do_page_fault+0x2a/0x90
 [] ? syscall_call+0x7/0xb
---[ end trace 9fd84e2ca1f666fb ]---

Edit /etc/modprobe.d/blacklist.conf file

vim /etc/modprobe.d/blacklist.conf

and add:

#  Cheesy workaround to clean up Dell PowerEdge 1750 boot
#  scb2_flash is not happy and causes a kernel oops and traceback
#  Not sure of the consequences of not having this and its associated modules loaded, but the machine boots cleanly
blacklist scb2_flash

Install Java SE Development Kit 7u40 on CentOS 6.4

Installing JDK on CentOS can be hard, so to help you I’ve made this simple tutorial. Hope it helps…

Download and install:

Go to an select JDK Download.

Install JDK:

rpm -ivh /path-to-file/jdk-7u40-linux-i586.rpm

And set it up:

alternatives --install /usr/bin/java java /usr/java/latest/jre/bin/java 20000
alternatives --install /usr/bin/javaws javaws /usr/java/latest/jre/bin/javaws 20000

Check if it is installed correctly:

java -version

Should return something like:

java version "1.7.0_40"
Java(TM) SE Runtime Environment (build 1.7.0_40-b43)
Java HotSpot(TM) Server VM (build 24.0-b56, mixed mode)


javac -version

Should return something like:

javac 1.7.0_40


Set JAVA_HOME variable:

echo "export JAVA_HOME="/usr/java/latest"" > /etc/profile.d/

Install Firefox browser support:

32-bit plugin:

alternatives --install /usr/lib/mozilla/plugins/ /usr/java/latest/jre/lib/i386/ 20000

64-bit plugin:

alternatives --install /usr/lib64/mozilla/plugins/ /usr/java/latest/jre/lib/amd64/ 20000


  1. Install Oracle Java JDK/JRE 7u25 on Fedora 19/18, CentOS/RHEL 6.4/5.9

SSL Certification Authority on Linux

SSL Certification authority

In cryptography, a certificate authority, or certification authority, (CA) is an entity that issues digital certificates. The digital certificate certifies the ownership of a public key by the named subject of the certificate. This allows others (relying parties) to rely upon signatures or assertions made by the private key that corresponds to the public key that is certified. In this model of trust relationships, a CA is a trusted third party that is trusted by both the subject (owner) of the certificate and the party relying upon the certificate. CAs are characteristic of many public key infrastructure (PKI) schemes.1


OpenSSL must be installed in order to create/manage certificates.

In the folder list I’m using ssl-name where name represents the entity that owns the CA.

Create folder structure

mkdir /etc/ssl-name
mkdir /etc/ssl-name/private
mkdir /etc/ssl-name/certs
mkdir /etc/ssl-name/crl
mkdir /etc/ssl-name/newcerts

Change default values in openssl.cnf

mkdir /etc/ssl-name
cp /etc/pki/tls/openssl.cnf /etc/ssl-name
vi /etc/ssl-name/openssl.cnf

In the following zones change the values:

mkdir /etc/ssl-name
[ CA_default ]

dir = /etc/ssl-name
certificate = $dir/certs/ca.crt
private_key = $dir/private/ca.key

[ req_distinguished_name ]

countryName_default = YOUR COUNTRY 2CHARS
stateOrProvinceName_default = YOUR PROVINCE NAME
localityName_default = YOUR LOCALITY NAME
0.organizationName_default = YOUR ORGANIZATION NAME
organizationalUnitName_default = YOUR ORGANIZATIONAL UNIT NAME
challengePassword_default = CHALLENGE PASSWORD
unstructuredName_default = SIMPLE NAMEFOR YOUR ORG

Initialize files with default values:

mkdir /etc/ssl-name
touch /etc/ssl-name/index.txt
echo '01' > /etc/ssl-name/serial
touch /etc/ssl-name/crlnumber
echo '00' > /etc/ssl-name/crlnumber

CA certificate

Generate CA certificate:

openssl req -config /etc/ssl-name/openssl.cnf -new -x509 -extensions v3_ca -keyout /etc/ssl-name/private/ca.key -out /etc/ssl-name/certs/ca.crt

Server Certificate

Generate a Certificate Request:

openssl req -config /etc/ssl-name/openssl.cnf -new -nodes -newkey rsa:2048 -keyout /etc/ssl-name/private/server.key -out /etc/ssl-name/server.csr -days 365

Be sure to type your service name correctly under the Common Name (CN) field (eg.

Sign the Certificate Request

You can sign the server certificate request by issuing the following command:

openssl ca -config /etc/ssl-name/openssl.cnf -out /etc/ssl-name/certs/server.crt -infiles /etc/ssl-name/server.csr


openssl ca -config /etc/ssl-name/openssl.cnf -policy policy_anything -out /etc/ssl-name/certs/server.crt -infiles /etc/ssl-name/server.csr

”-policy policy_anything” it means that the fields about the Country, State or City is not required to match those of your CA’s certificate (see /etc/ssl-name/openssl.cnf).

Two files were created:

  1. /etc/ssl-name/certs/server.crt – Server certificate.
  2. /etc/ssl-name/newcerts/01.pem – Same certificate, but with the certificate serial number as a filename.

You can now delete your certificate request file

rm -rf /etc/ssl-name/server.csr

Verify Server Certificate file

To check certificate basic info issue the following command:

openssl x509 -subject -issuer -enddate -noout -in /etc/ssl-name/certs/server.crt

To check certificate “useful” info issue the following command:

openssl x509 -in /etc/ssl-name/certs/server.crt -noout -text

To check certificate is still valid to use on a sslserver, issue the following command:

openssl verify -purpose sslserver -CAfile /etc/ssl-name/certs/ca.crt /etc/ssl-name/certs/server.crt

Revoke Server Certificate

To revoke the server certificate, issue the following command:

openssl ca -config /etc/ssl-name/openssl.cnf -revoke /etc/ssl-name/certs/server.crt

After each revocation you must generate a new CRL (Certificate Revokation List):

openssl ca -config /etc/ssl-name/openssl.cnf -gencrl -out /etc/ssl-name/crl/ca.crl

Be sure distribute the CRL file to those who trust your CA (eg. publish it online)

Server Certificate file misc.

To put the server certificate and key on the same file, issue the following command:

cat /etc/ssl-name/certs/server.crt /etc/ssl-name/private/server.key > /etc/ssl-name/private/server.pem

To convert the server certificate to DER format, issue the following command:

openssl x509 -in /etc/ssl-name/certs/server.crt -inform PEM -out /etc/ssl-name/certs/server.der -outform DER


Can I create my own S/MIME certificate for email encryption?
Email Certificates
Issue Your Own Self-Signed S/MIME Certs with OpenSSL
How do I create a valid email certificate for Outlook S/MIME with openssl?
How To Encrypt Mails With SSL Certificates (S/MIME)
Howto: Make Your Own Cert With OpenSSL