Did You Know? netcat is a unix utility which reads and writes data across network connections, using TCP or UDP protocol. It's designed to be a reliable back-end tool that can be used directly or easily driven by other programs and scripts. At the same time, it's a feature-rich network debugging and exploration tool, since it can create almost any kind of connection you would need and has several interesting built-in capabilities. Netcat, or "nc" as the actual program is named, should have been supplied long ago as another one of those cryptic but standard Unix tools.

Delivered by FeedBurner ISSN 1836-5930

Linux Tags

Poll

Which of following tutorials would you like to see on the Linuxconfig.org?

IP Addressing and Subnetting

SendMail server configuration

Introduction to the Python programming

Configuration of the SAMBA server

Howto deploy a custom iptables firewall

Working with emacs text editor

Configuring APACHE web server

KDE programming and application development

HowTo create a Debian package

usermod

Article Index
1. Name
2. Synopsis
3. Frequently used options
4. Examples

1. Name

usermod [man page] - modify a user account

2. Synopsis

usermod [options] LOGIN

3. Frequently used options

-e, --expiredate EXPIRE_DATE
      The date on which the user account will be disabled. The date is
      specified in the format YYYY-MM-DD.
-L, --lock
      Lock a user’s password. This puts a ’!’ in front of the encrypted
      password, effectively disabling the password. You can’t use this
      option with -p or -U.
-U, --unlock
      Unlock a user’s password. This removes the ’!’ in front of the
      encrypted password. You can’t use this option with -p or -L.

4. Examples

Lets see how we can lock account for user linuxconfig. This will add "!" into /etc/shadow for user linuxconfig. NOTE: this command requires superusers privileges.

# usermod -L linuxcofnig

usermod - lock user account
Now we can try login with user linuxconfig and see if that works:

usermod - login test
With a -U option we can unlock account:

# usermod -U linuxcofnig

Check if the "!" is removed from etc/shadow:

# grep linuxconfig etc/shadow | head -c 15 |  sed -e 's/$/\n/'

To make account expire we can use --expiredate option. This will expire user account on 1 January 2010.

# usermod --expiredate 2010-01-01 linuxconfig