mid 1960’s - Multics - proposed by AT&T, Honeywell, GE & MIT; funded by DARPA

1969 - Thompson & Ritchie create Unix

1978 to 84 - Bill Joy & Chuck Haley (Berkeley U.) create BSD Unix

Unix Wars I - BSD 4.2 versus System V

Unix Wars II - SVR4 versus OSF

ISO Standard - POSIX

1991 - Linus Torvalds creates Linux

BSDMachSystem V

HP-UXAIXOSF/1

SunOS

Solaris

NeXTStep

Free BSD

OS X

Linux

Authentication

Admin

File Systems

Network-related

Audit

UID

/etc/passwd UserName:*:UID:GID:FullName:UserDir:UserShell • entry:

GID

• passwords encrypted via crypt()• salt

• 16-bits• ID 0 - 99 reserved• ID 0 is root

• 16 or 32 bits• /etc/group stores local groups

• wheel group for system administrators

Standard UsersStandard Usersroot

- superuser account

daemon - executes as background process- handles system events such as print spooling

lp - print server process

guest - generic visitor account

nobody - default user for unprivileged access- user owns no files

mail - system account for email processing

sshd - for running secure shell tasks

www - for running a web server

shell

commands

• command line interface • Born (sh), c-shell (csh), tc-shell (tcsh)

• ls -- list directory information• cd -- set current directory• pwd -- display current directory• cat -- display contents of textfile

• whoami -- display current user• su -- log in as a different user (will be prompted for password)• man -- give help on command• sudo -- execute a single command as root (must specify password)

ufs

ffs

original Unix File System first tree-structured directory system

Fast File System allows longer file names (255 chars rather than 14) supports symbolic links

inodes separate inode (index node) per file/directory an inode has an address (index) but no name each inode resides on the disk contents: • address of associated item (file/directory)

• item type• item size (in bytes)• time of last inode modification• time of last modification of item (mtime)• time of last item access (atime)• reference count (number of names for this inode)• item’s UID• item’s primary GID

directory ...consists of a list of pairs: name - inode index

• item’s mode bits (permissions)

standard directory entries

shell commands

. refers to this directory’s inode.. refers to inode of the parent of this directory

• cp -- copy (duplicate) file• mv -- move file from one directory to another• mkdir -- create new directory• ln -- create new link (use -s flag for symbolic link)• rm -- remove one name• rmdir -- log in as a different user (will be prompted for password)

• chown -- change owner of file/directory• chmod -- change mode (permissions) for a file• umask -- set default mode (permissions) for this user

- rwx r-x --- t

- filed directoryc character device (tty, printer)b block device (disk, CD)l symbolic links socket

owner group world

Mode: 1000 - sticky bit2000 - set GID4000 - set UID 400 - read (owner) 200 - write (owner) 100 - execute (owner)

r readw writex executes set (in place of x)

Example

t “sticky” bit

TCP Wrappers

host-based firewalls

• a common way to secure network transmissions on some Unix versions• when tcp wrappers are turned on...

a) look in /etc/hosts.allow file for allowed firewall access

• results logged to syslog

b) look in /etc/hosts.deny file for denied firewall accessc) if no rules apply, then access is granted

• optionally sends banners to clients• can transfer access to “jail” or “faux”

• Free BSD• OS X• varies with Linux

echo (UDP Port 7)ping command sends datagram to test connectivity

systat (TCP Port 11)netstat command returns user names, login times, and so forth

ftp (TCP Ports 20 & 21)file transfer protocolftp transmits in plaintext - sftp encryptsanonymous ftp is a vulnerability

ssh (TCP Port 2)secure shell for remote loginuses symmetric encryption (ssh.config)requires that client have public key

telnet (TCP Port 23)original remote login shell - uses plaintext

smtp (TCP Port 25)Simple Mail Transfer Protocol - Internet standard for email transfer

dns (TCP & UDP Port 53)Domain Name System (stay tuned)

dhcp (UDP Ports 67 & 68)Dynamic Host Configuration ProtocolIP address leasing utility

finger (TCP Port 79)retrieves user info (name, location, login, telephone, and so forth

http (TCP Ports 80 & 443)HypterText Transfer Protocol (WWW protocol)

POP, POPS, IMAP, IMAPS (TCP Ports 109, 110, 143, 993 & 995)Post Office Protocol -- Internet Message Access Protocol

snmp (UDP Ports 161 & 162)Simple Network Management Protocolremote system management tool

rlogin & rsh (TCP Ports 513 & 514)more insecure login shellsempty /etc/hosts.equiv