Counting number of users in a group - Linux

Here is a small command to find number of users in particular group on a *nix system. An example for wheel group:

grep wheel /etc/group | fgrep -o , | wc -m

Now here's a catch, this command actually counts the commas in the line from the group file. So if there are 5 users in the group, the output will be 4. You will have to add a 1 to the output.

So when using it in scripts, one can use it like this:

VAR1=$(($(grep wheel /etc/group | fgrep -o , | wc -m) + 1))
echo $VAR1
5

Explanation:

First grep will print only the group and its members. The members are seperated by a comma. Next we print the commas using -o option and later count them using wc command. The second example will just add a 1 to it.

Let me know if you have a better idea for the same!

Kickstart and Hostnames

The basic purpose to use kickstarts is to install numerous systems at a time with given para.

Configuring each system post install is tedious.

I found a workaround (that worked for me on Oracle Linux 6 and RHEL 6 and should most probably work for similar distros) to automate this task post install as well. If you know better solution, drop a comment below.

In the %post% section,

Add this:

 exec < /dev/tty6 > /dev/tty6 2> /dev/tty6  
 chvt 6  

This will switch to the 6th TTY and will drop into interactive shell. This allows installer to ask for information.

Let's try to ask for information:

 echo -n "Enter Hostname: "  
 read HOSTNAME1  
 echo -n "Enter IP Address: "  
 read IPADDR  
 echo -n "Enter Netmask: "  
 read NETMASK  
 echo -n "Enter Gateway: "  
 read GATEWAY  

Now that we have information, we can use the inbuilt cmd to configure the interface. I assumed first interface as eth0 (which it is in most cases. If you are not sure, you might want to add this to automation to detect what interface you have).

  echo -n "Applying network settings..."  
 echo "DeviceList.Ethernet.eth0.BootProto=static  
 DeviceList.Ethernet.eth0.IP=$IPADDR  
 DeviceList.Ethernet.eth0.Netmask=$NETMASK  
 DeviceList.Ethernet.eth0.Gateway=$GATEWAY  
 ProfileList.default.DNS.Hostname=$HOSTNAME1.domain.com  
 ProfileList.default.DNS.Domainname=domain.com" > /tmp/network-config  
 system-config-network-cmd -i -f /tmp/network-config &> /dev/null  
 service network restart &> /dev/null 

The system-config-network-cmd helps us import /tmp/network-config file.
Restarting network service later loads the new configuration.

To drop out of the TTY 6 and resume back to anaconda use chvt trick again:

 chvt 1  
 exec < /dev/tty1 > /dev/tty1 2> /dev/tty1  

Credits for chvt trick: Hintshop blog.

Solving basics hell out of vsftpd

Configuring vsftpd isn't a very hard thing. If you haven't read the docs, then its crucial to go.

I had a fresh installation of vsftpd on CentOS 6.2

I tweaked hardly one or two params in /etc/vsftpd/vsftpd.conf such as "anonymous_enable=NO"

Then created a new user using:

 #useradd -m -d /home/user1 -s /bin/bash user1  

Then I tried to connect to the server using our brand new user1.
Here's what I got:
500 OOPS: cannot change directory :/home/user1

After a bit digging on Google and thanks to this link, I was able to do it when I ran following command:

 /usr/sbin/setsebool -P ftp_home_dir 1  

This command takes a while to run, but it worked for me after that.
The setsebool sets boolean variables in SELinux.

Stopping OpenLDAP

This is most dumb but useful post. How to turn off slapd.

You know how to start the slapd:

 #/usr/local/libexec/slapd  [-option..]

however, pkill slapd is not the correct way to turn off slapd.

Here's how you turn it off:

 #kill -INT `cat /usr/local/var/slapd.pid`  

This will send appropriate signal to slapd process, and will store any cached data and close gracefully.

OpenLDAP 2.4 on CentOS 6.2 Part 1

It is painful when you have errors and somehow you aren't getting way around it.

Here's how I did my Installation:

Downloaded Latest release of OpenLDAP (2.4.31) from here.

Transferred the file to the CentOS 6.2 Server using Secure Copy (SCP). The directory on server can be any with sufficient space in it. I used /home.

The downloaded package was openldap-2.4.31.tgz.
Extract it.

 # tar -xvf openldap-2.4.31.tgz  

This will create a directory /home/openldap-2.4.31
cd to that Directory.

Here you will have some files including the "configure" script.
To check what options the script provides, perform following command

 #./configure --help  

It is always better to let the script decide what options are best for you. We will choose options later as required.

 #./configure

It will start to configure the build.

Here's first error I encountered:

configure: error: Unable to locate cc(1) or suitable replacement.  Check PATH or set CC.

Then I did

 yum install gcc

Which installed development tools, C compiler etc.

The next error, most common:

configure: error: MozNSS not found - please specify the location to the NSPR and NSS header files in CPPFLAGS and the location to the NSPR and NSS libraries in LDFLAGS (if not in the system location)

Location for NSPR and NSS Libraries and Headers varies with Operating System. However, I was unable to find that. I will update soon as soon as I find it.

I tried following option

 #./configure --with-tls=no  

This option bypassed the tls check.

WARNING: Your LDAP Server will then be unable to have TLS Data Protection.

The next error:
configure: error: BDB/HDB: BerkeleyDB not available

This made me download and install BerkeleyDB from here.
To install Berkeley DB see the documentation. I copied it to /home and installed it as follows:

 #tar -xvf db-5.3.21.gz  
 #cd db-5.3.21  
 #make  
 #make install  

Even after installing Berkely DB, it didn't let me proceed with same error. What was missing?
Well I set a few Variables, and I was off.

 CPPFLAGS="-I/usr/local/BerkeleyDB.5.3/include"  
 export CPPFLAGS  
 LDFLAGS="-L/usr/local/lib -L/usr/local/BerkeleyDB.5.3/lib -R/usr/local/BerkeleyDB.5.3/lib"  
 export LDFLAGS  
 LD_LIBRARY_PATH="/usr/local/BerkeleyDB.5.3/lib"  
 export LD_LIBRARY_PATH  

Make sure you put a capital "I" instead of "i" in CPPFLAGS or it may throw following error:


configure:5251: error: C compiler cannot create executables
See `config.log' for more details.

Then the harsh configure was done.
Next command, Run "make depend", then "make", then "make test" and last "make install"!

Continuing in Part 2, the configuration after installing OpenLDAP.

Print first column of passwd

The delimiter used to differentiate different fields in the /etc/passwd files is colon ' : ' . Therefore we need to look only after the semicolon.

To deal with column based files or formatted text the most commonly used command is awk.

Command below will print out the first column of /etc/passwd file:

 awk < /etc/passwd -F: '{ print $1 }'

Here

awk             is the text processor

< /etc/passwd    will serve as input file for awk

-F:             is a parameter for awk that specifies the delimiter. In our      
                           case is colon.

{ print $1 }    This will print the first line. You can put $2, $3 etc. to
                           print respective column.

My command produced following output:

 root  
 daemon  
 bin  
 sys  
 adm  
 lp  
 uucp  
 nuucp  
 smmsp  
 listen  
 gdm  
 webservd  
 postgres  
 svctag  
 nobody  
 noaccess  
 nobody4