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
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