UNIX®

In the old days, there was Solaris, HP-UX, and AIX (in the really old days there was AT&T Unix).  These days the most popular UNIX flavors are Linux and BSD based (for example, Apple's MacOS X is based on BSD, Juniper's JunOS is also based on BSD and Cisco's NX-OS is based on Linux).

Linux Distro's:

Commercially supported:

Red Hat Enterprise Linux:         http://www.redhat.com

Novell Suse Linux Enterpirse:   http://www.novell.com/linux/

Community supported:

Red Hat Fedora:                        http://fedoraproject.org/

CentOS (based on RHEL):        https://www.centos.org/

OpenSuse:                                http://www.opensuse.org

Mandriva:                                  http://www.mandriva.com/

Debian:                                     http://www.debian.org/

Ubuntu:                                     http://www.ubuntu.com/

Note that technically Linux is just the Linux kernel.  All the other software is part of that Linux distribution.  For more distributions, see: http://en.wikipedia.org/wiki/Linux_distribution

Also note that Ubuntu, Mandriva, etc, you can get commercial support if you want it, but you don't have to pay for support to get updates.  Oracle now owns Sun with the SPARC chip, who knows where that is going; and IBM has its own world of CPU's and OS's.  Oracle/Sun still runs OpenSolaris, the x86 version of Solaris, which is notable in that you can choose it as an OS in the Amazon EC2 cloud:

http://www.opensolaris.com/

BSD:

BSD is not in the spotlight, but behind the scenes is still a huge part of the UNIX world.

Apple Mac OS X is based on BSD:     http://www.apple.com/macosx/developers/

FreeBSD: http://www.freebsd.org/

NetBSD: http://www.netbsd.org/

OpenBSD (also the source of openssh, openssl): http://www.openbsd.org/

UNIX Commands:

File Archiving/Package installation:

tar archives:

tar -ztvf           list files in archive

tar -zxvf          extract files in archive

RPM:

rpm -Uvh           upgrade rpm package

pkgadd/pkginfo    Solaris packgage commands

Find/locate:

find / -name '*whatever*' -print

locate x        where x =filename, in linux, updated periodically or can run updatedb

whereis

other:

crontab -l           list crontab for current user

crontab -e          edit crontab for current user

df -k                   disk free in KBytes

df -i                    inode's free

for more see:

http://www.redhat.com/docs/manuals/linux/

http://www.kernel.org/

http://www.rpmfind.net/

http://www.tldp.org/ The Linux Doc. Project

Typical UNIX directory structure:

/ root directory

/dev direct access to hardware devices

/bin system executable files

/sbin sysadmin executable files

/etc config files

/lib shared libraries

/usr/bin executables not needed at boot

/usr/sbin sys admin executables not needed at boot

/usr/lib shared library files

/usr/include shared header files

/usr/local user installed programs/executables

/var/log log files

/var/spool print spooling, mail spooling, etc.

/var/mail mail files

/mnt where local and network drives get mounted

Legal stuff:

UNIX® is a registered trademark of The Open Group in the United States and other countries. Linux is a trademark of Linus Torvalds;RedHat and RPM are trademarks of RedHat,Inc.