Transcript UNIX - SigmaNet

Unix Administration
Guntis Barzdins
Linux System Administration
SYS ADMIN TASKS
Setting the Run Level
System Services
User Management
Network Settings
Scheduling Jobs
Quota Management
Backup and Restore
Adding and Removing software/packages
Setting a Printer
Monitoring the system (general, logs)
Monitoring any specific services running. Eg. DNS,
DHCP, Web, NIS, NPT, Proxy etc.
Have you used UNIX before?
• Which OS did Apple choose
when it needed a stable OS layer
for its Mac OSX?
• Which OS made the biggest
impact to the online lives as you
know it today?
Process Manipulation
 Once you run a program (e.g. vi, myprog,...), that program
will suspend the terminal you called it in (the terminal will
not be receiving input from you).

You can start the program in the background to avoid this:


myprog &
You can suspend a program that is running and send it to background, if you already
started it:


Ctrl-z (to suspend)
bg (sends the suspended program to the background)



ps (show running processes)
top (monitor running processes)
kill (kill processes)




& (send process to background)
bg (send process to background)
fg (get process from background)
Ctrl+c (terminate process)
Intrusion Detection System (IDS)
Open Source Tripwire – is a file integritychecking program for UNIX/Linux
operating systems

Host-based

Software that alerts you when important files change

Tripwire keeps a hash value for each designated file


When a file is altered/deleted, tripwire will have a new hash value that is
different than the original
Replaced by more advanced HIDS: OSSEC, Samhain, AIDE
Tripwire tutorial in a slide
 Initial setup


download / build / install it
modify policy file (e.g. remove unnecessary files)
# vi /etc/tripwire/twpol.txt

generate policy file
# twadmin –create-polfile /etc/tripwire/twpol.txt

build initial database
# tripwire –init
 check periodically
# tripwire –check
 reconcile differences (e.g. software installation)
# tripwire –update –accept-all –twrfile report_file
Linux Security
LINUX Firewall
Linux Security
SELinux
Originally created by NSA to meet US DoD MAC
Malicious or broken software can have root-level
access to the entire system by running as a root
process.
SELinux (Security Enhanced Linux) provides
enhanced security.
Through SELinux policies, a process can be granted
just the permissions it needs to be functional, thus
reducing the risk
SELINUX can take one of these three values
enforcing - SELinux security policy is enforced.
Linux Security
SELinux Configuration
AppArmor
Less complex and less secure
Popular in user oriented distributions (Ubuntu, SUSE),
enabled for some potentially vulnerable services by default
Bundle software packages with AppArmor profiles
Can create profile file by launching application in
learning mode, can make secure enough profile if
application not already compromised
Capabilities: FS open/read/write different modes,
networking (all/tcp/udp), executability etc.
Log files
 On linux, you can go to /var/log
 Depends on the application
 Information shown in log files depend on the
debug level you defined
Linux System Administration
Configuring Disk Quotas
To implement disk quotas, use the following steps:
Enable quotas per file system by modifying /etc/fstab
Remount the file system(s)
Create the quota files and generate the disk usage
table
Assign quotas
Linux System Administration
Configuring Disk Quotas
Enabling Quotas: Edit fstab to enable usrquota
LABEL=/1
LABEL=/boot
LABEL=/users
LABEL=/var
LABEL=SWAP-sda5
/
/boot
/users
/var
swap
ext3 defaults
ext3 defaults
ext3 exec,dev,suid,rw,usrquota
ext3 defaults
swap defaults
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12
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Linux System Administration
Configuring Disk Quotas
Remounting the File Systems: Issue the umount
command followed by the mount command to
remount the file system in which quota has been
implemented (umount /users;mount /users)
Creating the Quota Database Files: Use quotacheck
command to create quota.user file
quotacheck -cu /users
Assigning Quotas per User: assigning the disk quotas
with the edquota command (edquota <username>)
Disk quotas for user web_cc (uid 524):
Filesystem
blocks
soft
hard
hard
inodes
soft
Linux Commands
Linux Filesystem Management
badblocks Used to search a disk or partition for
badblocks. (badblocks device) (badblocks hda)
df Shows the disk free space on one or more
filesystems. (df –k, df -h)
du Shows how much disk space a directory and all its
files contain. (du <directory>, du –sk <directory>, du –
sh <directory>)
 Find out which users use most space etc.
 $ du /home -d 1 | sort
fsck Filesystem check. Must not be run on a mounted
file system. (fsck <filesystem>)
Linux Commands
Linux Filesystem Management
sync Synchronize data on disk with memory. `sync'
writes any data buffered in memory out to disk.
mount Used to mount a filesystem. Complement is
umount. (mount <filesystem>, mount –a)
umount Unmounts a filesystem. Complement is
mount. (umount <filesystem>)
Native UNIX Backup Utilities
 UNIX Systems include 3 core utilities
that allow you to backup files to tape
or disk.

tar (very simple to use)

cpio (a bit more complex)

dump (most complex of the three)
Using the tar Utility for Backup
 tar usage:
tar [x|c]vf [tape device name] [files or
directory]
 Where:

x = extract from a tape

c = compress onto tape

j = use bzip compression

z = use gzip compression
(just like when we tar and untar regular .tar files)
Other UNIX Backup Utilities
 cpio – has the ability to detect I/O errors
during backup that tar cannot detect. Also
has the ability to do things like specify
wildcard patters during restore.
 dump – very fast, detects I/O errors, allows
you to perform incremental backups.
TAR
CPIO
DUMP
Simplicity of Invocation
Very Simple
(tar c files)
Needs find to specify file names
Simple. Few Options
Recover from I/O errors?
None. Write your own utility
Resync Option on HP-UX will cause some data loss
Automatically skips over bad section
Backup special files
Later Revisions
Yes
Yes
Multi-volume backup
Later Revisions
Yes
Yes
Backup across network?
Using rsh only
Using rsh only
Yes
Append files to backup
Yes, (tar –r)
No
No
Multiple Independent Backups on Single Tape
Yes
Yes
Yes
Ease of listing files on the volume
Difficult, Must search entire backup
( tar –t )
Difficult, Must search entire backup
( cpio –it )
Simple, Index at front
( restore –t )
Ease and speed of finding a particular file
Difficult, No wildcards, Must search entire volume
Moderate, Wildcards, Must search entire volume
Interactive. Very easy with commands like cd, ls
Incremental backup
No
Must use find to locate new/modified files
Incremental of whole filesystem only, Mult. Levels
List files as they are being backed up
tar cvf 2>logfile
cpio –v 2>logfile
Only after backup with restore –t >logfile
(Dump can show % complete, though.)
Backup based on other criteria
No
Find can use multiple criteria
No
Restore absolute path names to relative location
Only by using chroot
Limited with cpio -I
Always relative to current working directory
Interactive decision on restore
Yes or No possible with tar –w
Can specify new path or name on each file
Specify individual files in interactive mode
Compatibility
Multiple platform
Multiple platform with ASCII header, not always
portable
Readable between some platforms, but cannot be
relied on
Primary usefulness
Individual user backup, transfer files between
filesystems
System backup, transfer files between filesystems
System backup
Volume efficiency
Medium, usually limited to 10k block size
Medium, usually only 5K block size, but can specify
larger size on some OSs
High, can usually specify up to maximum block size of
device
Wildcards on restore
No
Yes
Only in interactive mode
Simplicity of selecting files for backup from numerous
directories
Low, must specify each independent directory,
subdirectories included
Medium, find options
None, will backup one and only one filesystem
Specifying directory on restore get files in that
directory
Yes
No, must use "path/*"
Yes
Stop reading tape after a restored file is found
No
No
Will stop reading tape as soon as last file is found
Track deleted files
No
No
If you restore with –r, files deleted before last
incremental dump will be deleted.
Filesystem efficiency
Better
Worst (files get a stat from both find and cpio)
Best
Limit on path length
(Tests done with Solaris native utils 7/99.)
155 characters. Complains "prefix is greater than 155
characters." Gtar has slight workaround.
255 characters. Doesn’t complain. Just truncates
pathname to 255 char’s.
1056 characters.
Likelihood that file exists in TOC but not in archive
Low
Low
Medium (since TOC is made first)
rsync
 Over network and filesystem
 Secure through SSH

Both ends require rsync executable, no services or daemons required
 Incremental backup
 Delta encoding

Only changed parts of files transmitted
 Example

rsync -avz [email protected]:/home /backups/server1
 Many options
Lost Root Passwd
 If you have Lilo installed, type


LILO: linux init 1
Change the root passwd, reboot again
 If you have installed grub

Type ‘e’ to go to edit mode, add init 1 argument at the end
 Boot with LiveCD (default Ubuntu etc.)




Mount the disk
chroot into mounted disk
passwd
Reboot and remove CD
Linux System Administration
Linux Services
There are 113 daemons, Out of them, the following
are most widely used:
apmd : Power Management
autofs : Automount services
crond : Periodic Command Scheduler
cups : Common Unix Printing System
dhcpd : The DHCP server
dovecot : IMAP (Internet Message Access Protocol)
and POP3 (Post Office Protocol) server
gpm : Mouse
httpd : Apache Web server
Linux System Administration
Linux Services
iptables : Kernel based Packet Filtering firewall
kudzu: Finds new Hardware
mysqld : MySQL server
named : BIND server
network : Networking
nfs : Network File Share
nfslock : NFS file locking
ntpd : NTP (Network Time Protocol) server
portmap : RPC (Remote Procedure Call) support
postgresql : The Postgresql Database Engine
Linux System Administration
Linux Services
sendmail : Sendmail Mail Server
smb : Samba Network Services
snmpd : Simple Network Management Protocol
squid : Squid Proxy Server
sshd : Open SSH and SFTP server
syslog : System Logging
xinetd : Provides support for telnet, ftp, talk, tftp etc.
ypbind : NIS Server
Automating Unix
Administration
 You don’t want to spend the whole day making sure
that all servers/workstations and its services are
fine
 Use monitoring tools that can alert you for any
problem in the network


mon, nagios, cacti, angel
Zabbix – Latvian product
 Create scripts to check the status of servers/services
and use cron to run it periodically

Mail the result to admin
Example script
#!/bin/sh
machine="sunfire"
down=
i=0
while [ $i -le 15 ]
do
sun=$machine"$i"
/usr/sbin/ping $sun > /dev/null
if [ $? -ne 0 ]
then
down="$down:$sun"
fi
i=`echo "$i+1" | bc -l`
done
if [ -n "$down" ]
then
echo $down | tr : '\012' | /usr/ucb/mail -s "DOWN machines"
[email protected]
fi
exit 0
NFS Architecture
VFS layer hides differences between
OS’s

It doesn’t matter what OS the client or server implements, UNIX
or Windows. As long as the file systems are compliant with the
file system model offered by NFS.
Operations on VFS are either passed
to local FS or to NFS Client, which
handles files at the remote server.
All client-server communication is
done through RPCs, with client and
NFS Architecture
Stateless vs. Stateful
NFS (Network File System)
RCP request
Action
Idempotent
GETATTR
Get file attribute
YES
SETATTR
Set file attribute
YES
LOOKUP
File name search
YES
ACCESS
Check access
YES
READLINK
Read from symbolic link
YES
READ
Read file
YES
WRITE
Write to the file
YES
COMMIT
Fix server cache data to the disk
YES
CREATE
Create file
NO
REMOVE
Remove file
NO
RENAME
Rename file
NO
NFS (Network File System)
RCP request
Action
Idempotent
LINK
Create hard link
NO
SYMLINK
Create symbolic link
NO
MKNOD
Create special node
NO
MKDIR
Crate directory
NO
RMDIR
Remove directory
NO
READDIR
Read directory
YES
READDIRPLUS
Extended directory read
YES
FSSTAT
Get FS dynamic attribute
YES
FSINFO
Get FS static attribute
YES
PATHCONF
Get POSIX information
YES
NFS (Network File System)

Stateless protocol problems:




Local file systems have state.
Shared lock’s implemented by user space daemon rcp.lockd
Performance problems, because all file system modification
commands should be fixed on disks before RPC request can be
positively answered. In most cases it is 3 I/O operations.
In NFSv3 protocol there is asynchronous writes. Implemented using
cookies to control server state during asynchronous writes.
FreeBSD NFS implementation
There are 3 type of leases:



Non-cache lease – define that all file system operations
should be take synchronously with server
Read cache lease – let client cache data, not allow to change
file.
Write cache lease – let client to cache write operations for
lease time. So if client cache write data, then this data will not
be written to the server synchronously. When lease time
coming to the end client will try to get another lease, but if it’s
not possible, then data have to be written to the server.
FreeBSD NFS implementation (read cache lease)
Server
Client A
Read sys. call
Read req. + lease
Read sys. Call
(from cache)
Answer
Read req.
(cache miss)
Lease timeout
Read sys. call
ctime the same cache valid
Read sys. Call
(from cache)
Answer
Read cache lease
for client A
Time
Lease expired
Read lease req.
Answer with
same ctime
Read req.
(cache miss)
Answer
Lease timeout
Client B
Read req. + lease
Answer
Client B added to lease
Read sys. call
Read sys. call
Read req.
(cache miss)
Answer
Lease timeout
FreeBSD NFS implementation (write cache lease)
Server
Client B
Write cached lease
Write cached lease
for client B
Lease update
Answer
(write cache lease)
Get record
lease
Answer
(write cache lease)
Write system call
Write system call
(cached leaved records)
Write cached lease
req. before previous lease
expired.
System call
Lease timeout
Lease expiration
Stopped for a
moment because
of records
Write_slack seconds
After last records
record
Lease expired
answer
record
Time
answer
FreeBSD NFS implementation (non-cache lease)
Client A
Read sys. call req.
Read req.
(from cache)
Read req. + lease
Time
Read cache lease
for A client
answer
Read req.
(miss cache)
answer
Lease timeout
Read sys. call req.
Client B
Server
Lease expired
Get write cache lease
Write sys. call req.
Write sys. call
(async write cached)
Lease request
Cleanup req.
record
record
Read sys. call req.
(non-cache lease
mode)
Answer (non-cache lease)
Read req.
Read data
answer
Release msg. answer
Get write cache lease
Write cached
data to server
Write sys. call req.
Answer (non-cache lease)
record
answer
Synchronous
Writes wihout cache
Starting up NFS
 There are three key things you need to start on Linux to
make NFS work.



/usr/sbin/rpc.portmap
/usr/sbin/rpc.mountd
/usr/sbin/rpc.nfsd
 These things should start up automatically at boot time.

The file that makes this happen is "/etc/rc.d/rc.inet2"
rpcinfo -p localhost
program vers proto
100000
2
tcp
100000
2
udp
100005
1
udp
100005
1
tcp
100003
2
udp
100003
2
tcp
port
111
111
679
681
2049
2049
portmapper
portmapper
mountd
mountd
nfs
nfs
Exporting File System
 To make parts of your file system accessible
over the network to other systems

The /etc/exports file must be set up to define which of the local
directories will be available to remote users and how each is used
# sample /etc/exports file
/home/yourname 192.168.12.1(rw)
/master(rw) trusty(rw,no_root_squash)
/projects proj*.local.domain(rw)
/usr *.local.domain(ro) @trusted(rw)
/home/joe pc001(rw,all_squash,anonuid=150,anongid=100)
/pub (ro,insecure,all_squash)
/pub/private (noaccess)

stop and restart the server
# etc/rc.d/init.d/nfs stop
# etc/rc.s/init.d/nfs start
39
The NFS Server
 Started though rc script:
/etc/rc.d/init.d/nfs
Must be started after:
/etc/rc.d/init.d/portmap
 Uses these RPC daemons in /usr/sbin:




rpc.nfsd – main component of NFS system
rcp.mountd – handles mount requests
rpc.quotad – allows for quota enforcement via NFS.
All of which are started in the nfs rc script when the system starts
 /etc/exports – the main server configuration
file
 Above utilities are part of knfsd package .rpm
package on Linux.
/etc/exports
 Contains information about the directory paths
and partitions that are sharable and hosts they can
be shared with.

i.e. “Any host from .rutgers.edu can access the /home/documents
directory on my server”
 Entry format:
/dir/to/export client1(permissions) client2
(permissions)
Sample entry:
/tmp iti.rutgers.edu(rw) 185.14.237.4(ro)
 Need to run exportfs to inform NFS server process
about changes in /etc/exports:
> /usr/sbin/exportfs –a (exports all entries)
The NFS Client
 Requires knfsd-clients .rpm package on Linux.
 Necessary services started from:
/etc/rc.d/init.d/nfslock
 RPC daemons in /sbin handle file locking between
client and server:



rpc.locked
rpc.statd
All are started from the nfslock rc script automatically
 Allows clients to mount remote file systems either
using the mount command or by placing an entry in
the /etc/fstab file.
Local and remote file systems accessible on
an NFS client
Serv er 1
Client
Serv er 2
(root)
(root)
(root)
export
...
v munix
usr
nfs
Remote
people
mount
Remote
s tudents
x
s taff
big jon bob . . .
mount –t nfs Server1:/export/people
mount –t nfs Server2:/nfs/users
mount
users
jim ann jane joe
/usr/students
/usr/staff
FUSE (Filesystem in Userspace)
Lets non-privileged users create their
own file systems without editing
kernel code.
FUSE
 Allows to implement anything with file
write and read operations and provide it
as file system
 Encryption – EncFS, TrueCrypt, etc.
 Network protocols – SSH, FTP, SFTP, etc.
 Cloud storage – Dropbox and every other
kind
 RAM disk
SMB
 SMB is Microsoft’s protocol to share files and printers




Also renamed CIFS (Common Internet File System)
Client/Server, no location transparency
Not the same as Samba: an open source implementation of SMB primarily
found on UNIX systems (Linux)
SMB usually runs on NetBIOS (naming + sessions + datagram)
 NetBIOS + SMB developed for LAN use
 A number of other services run on top of SMB


In particular MS-RPC, a modified variant of DCE-RPC
Authentication for SMB handled by the NT Domains
suite of protocols, running on top of MS-RPC
NT-Domain
MS-RPC
SMB
NetBIOS
TCP/IP
To know more: Timothy D Evans, NetBIOS, NetBEUI, NBF,
NBT, NBIPX, SMB, CIFS Networking
Samba Services
 File sharing.
 Printer sharing.
 Client authentication.
SMB Protocol
 Request/response.
 Runs atop TCP/IP.
 E.g., file and print operations.

Open close, read, write, delete, etc.

Queuing/dequeing files in printer spool.
Network Booting
 No need for harddisk(or harddisk with
Linux) on every host
 High level work flow

The system boots up, may be with floppy (could be with hard disk also)

Sends dhcp request for IP number, gets one

Mounts the root file system over NFS
Requirements for Network
Booting




Setup an LAN infrastructure
Need to setup nfs server
Need to setup dhcp server
Build a kernel image for network
booting
Setup an LAN infrastructure
Ethernet
Cable
Your m/c to be booted
Hub
Ethernet
Cable
NFS server
Your host, NFS server and DHCP server should be on
same LAN
Setup nfs server
• Edit /etc/exports file before starting the nfs
server.
•
•
/ 10.114.7.115(rw,no_root_squash)
This will export all files with root r/w to host
10.114.7.115
• Save your exports file and from the prompt
execute exportfs command
• Start the nfs server (nfs daemon)
•
E.g. /etc/rc.d/inid.d/nfs start
Setup dhcp server
 Add in your /etc/dhcpd.conf before starting the dhcp server.
 Set the correct MAC address in /etc/dhcpd.conf as follows:
subnet <subnet address e.g.10.3.31.0> netmask 255.255.255.0 {
}
subnet 10.10.10.0 netmask 255.255.255.0 {
host master {
hardware Ethernet <Mac address of your Ethernet card>;
fixed-address <IP address of your machine e.g.10.10.10.1>;
option root-path <your root path>”;
}
}
 Save your /etc/dhcpd.conf file
 start the dhcpd dameon by “/etc/rc.d/init.d/dhcpd start”
command
Build a kernel image for network
booting
 Linux Kernel compilation steps:

Assumptions: machine x86 (i386); boot loader lilo.

Get plain vanilla kernel from www.kernel.org

Explode it into a directory (better if can do it in /usr/src/) => tar -zxvf linux-2.x.xx.tar.gz

Optional: create a symbolic link ln -s linux-2.x.xx linux

cd to linux directory

cd /usr/src/linux or cd /usr/src/linux-2.x.xx

Select the components support by make menuconfig or make xconfig - save the
configuration


Select IP:BOOTP support from Networking options
In File system -> Network File System -> Select
 NFS File system support and
 Root file system on NFS

Do


Make dep bzImage
Make modules modules_install
Build a kernel image for network
booting…
 Copy the
/usr/src/linux/arch/i386/boot/bzImage
to /boot
 Do mkbootdisk with new kernel as
argument
 Optional take a coffee or tea break ?
Just imagine if one day...
Your CEO announces:
• Company is changing name from "Windoze" to "UsefulNix"
• TOMORROW!
Your "small part":
• Update the company website* to reflect that!
Can you deliver this in time?
*: About 20,000 html files.
Demo (1/2)
- UNIX vs. Window
• Task 1 : Open a file. Find occurrences of "Windoze".
 Windows: use Ctrl-F at any text editor.
 UNIX: grep -l Windoze fileName
• Task 2 : Find all files in folder A containing "html".
 Windows: Arggghhhh!!! Open all files and check?
 UNIX: find A -type f | xargs grep -l Windoze
Demo (2/2) - UNIX vs. Window
• Task 3 : Open a file. Replace "Windoze" by "UsefulNIX"
 Windows: Use Ctrl + H at any text editor
 UNIX:
perl -pi -e 's/Windoze/UsefulNIX/g'
fileName
• Task 4 : Find all files in folder A with "html", and replace by
"UsefulNIX"
 Windows: haizzz....
 UNIX: find A -type f | xargs grep -l Windoze |
xargs perl -pi -e 's/Windoze/UsefulNIX/g'
See how powerful UNIX is ^^ & the idea of "achieving complex tasks
through small toys“
Let's learn UNIX !!!