Linux Quota Support

http://www.yolinux.com/TUTORIALS/LinuxTutorialQuotas.html

mdadm software raid usage

Install
mdadm package needed (aptitude install mdadm)
http://neil.brown.name/blog/mdadm

Create array:
mdadm --create --verbose /dev/md0 --level=0 --raid-devices=2 /dev/sdb1 /dev/sdc1
or
mdadm -Cv /dev/md0 -l0 -n2 -c128 /dev/sdb1 /dev/sdc1

/etc/mdadm.conf
# optional, but used for easier interaction
DEVICE /dev/sdb1 /dev/sdc1
ARRAY /dev/md0 devices=/dev/sda1,/dev/sdb1

Show md info:
# produces output that you would put in the mdadm.conf
mdadm --detail --scan

Show device info:
mdadm -E /dev/sdc1
# shows info about the component disks

Start (assemble) Existing Array:
mdadm -As /dev/md0
# -A starts assemble mode to assemble existing array
# -s indicates the use of /etc/mdadm.conf
or
mdadm -A /dev/md0 /dev/sdb1 /dev/sdc1
# starts array without existing /etc/mdadm.conf

Assemble an existing array automatically:
mdadm --assemble --scan
or
mdadm -As

Stop the array:
mdadm -S /dev/md0
or
mdadm --stop /dev/md0

Add a disk:
mdadm /dev/md0 --add /dev/sdc1

Remove a disk:
mdadm /dev/md0 --fail /dev/sdc1 --remove /dev/sdc1
# "fails" and removes a disk

fstab entry for the array:
# this assumes the array was formated with ext3
/dev/md0 /export/ ext3 suid,dev,defaults,exec 0 0


http://www.linuxdevcenter.com/pub/a/linux/2002/12/05/RAID.html

SUDO

Generic syntax of /etc/sudoers
<users_to_allow> <host> = (run_as_user) <command_to_run>
<users_to_allow> <host> = (run_as_user) <file_to_grant>

No password for users in admin group
%admin ALL= (ALL) NOPASSWD: ALL

No password for joeuser user
joeuser ALL=(ALL) NOPASSWD: ALL

Allow joeuser to run only certain privileged commands as root
joeuser ALL= /bin/kill, /usr/local/bin/

Allow joeuser to run certain commands as given users
joeuser ALL=(janeuser,johnuser) /bin/kill, /usr/local/bin

Run sudo command as another user using
sudo -u janeuser /bin/kill

http://aplawrence.com/Basics/sudo.html

Screen Command Usage

Create a new Screen session
screen # creates a default session
screen -S name # creates a session with a name

# Screen has two similar concepts: screens and window sessions.
# screens are seperate processes that show up when doing
# a "screen -ls" listing. Windows are "sub-screens" of a given
# screen process used for split screen modes and such.

Rename an already created window
CTRL-a A # then provide name

Rename a screen (interactively)
CTRL-a :sessionname newsessionname

Rename a screen (without attaching)
screen -X sessionname newsessionname

Detach from a screen session
screen -d # detach from a command prompt
Ctrl-a d # detach from anywhere in the session

List screen sessions
screen -ls

Reattach to a screen session
screen -r # attaches to default session
screen -r name # attaches to specific session (unique string in the name)

Toggle between several attached windows
Ctrl-a Ctrl-a

Attach to an already attached screen (mirror)
screen -x # attaches to default session
screen -x name # attaches to named session

Share a screen session
owner:
screen -S name # start and name the screen
Ctrl-a :multiuser on # add multiuser support
Ctrl-a :acladd userids # share the screen to userids (comma sep)

client:
screen -x username/session # attach to the screen (in mirror)

Change permissions on a shared session
owner:
Ctrl-a :aclchg userids [permbits] [list]
# permbits = rwx and prefixed by "-" or "+"
# list of commands - #(all windows), ?(all commands)

Remove user access
owner:
acldel userids

Lock a Screen
ctrl-a ctrl-x # requires user to enter password to unlock

Copy and Paste from the screen scrollback buffer
Ctrl-a [Esc] # enters scrollback editor (movement like vi)
[spacebar] # starts and stops a copy selection range
Ctrl-a :paste . # pastes the copy buffer to the term

Screenrc options:
/home/> vi .screenrc
#shell -bash
shell -ksh # Make Screenrc exe .profile file on login

# Set the scrollback buffer
defscrollback 5000

# Turn off the startup banner
startup_message off

# displays a status line at the bottom of the terminal window.
hardstatus alwayslastline "Screen: %w %c:%s %D, %M/%d/%Y "

# detach on hangup - if my dial-up session fails, screen will simply
# detach and let me re re-attach later
autodetach on

Split Screen
# Create two screens
screen # create first screen
CTRL-a c # create second screen session (1 screen instance, but 2 window sessions)
CTRL-a S # split the screen
CTRL-a TAB # move to the bottom part of the split
CTRL-a " # will prompt for a screen number. Choose 0 or 1 indicating the window session
CTRL-a Q # quit all splits except the current

Scrollback / Copy and Paste
CTRL-a [ or CTRL-a ESC # frees the cursor to move into scrollback buffer (Copy mode)
# ESC to exit copy mode without copying
# use arrow keys or h,j,k,l to navigate in copy mode
# use CTRL-F and CTRL-B to page up and down in copy mode
ENTER # indicates a start point for text copy
ENTER # (second) indicates an end point for text copy
CTRL-a ] # pastes copied text range

http://aperiodic.net/screen/quick_reference
http://news.softpedia.com/news/GNU-Screen-Tutorial-44274.shtml

SSH Port Forward

Allow port forwarding on the server
# Edit the /etc/ssh/sshd_config
AllowTcpForwarding yes

Local Forward
# create a tunnel to access an ssh server behind a firewall using a gateway
ssh -L 7777:192.168.1.160:22 gateway.example.com cat -

# access the ssh server via your local machine
ssh -p 7777 localhost

http://www.securityfocus.com/infocus/1816

Find File Space Usage

Find space used on filesystem level:
du -ks # shows summary of space used on disk in Kb
du -ms # shows summary of space used on disk in Mb
du -gs # show summary of space used on disk in Gb

Find space used on a file level:
find . -type f -ls | awk '{print $7}' | while read size
do
((TSIZE=TSIZE + $size))
done
echo "$TSIZE"

Shows largest files in a directory:
ls -l | sort -k 5rn,5 -k 9fd,9
-k = search criteria
5 = sort column five
r = apply reverse sort
n = numeric sort

Shows files using the most space on the filesystem:
du -ak | sort -k 1rn -k 2fd

Shows users using the most space:
# this space list will not include files or dirs that the current
# user has no read permissions on
ls /home/ | while read a
do
du -sm /home/$a
done 2> /dev/null | sort -k 1n | tail -10


http://www.devdaily.com/unix/edu/examples/sort.shtml
http://www.cs.rit.edu/~vcss231/Labs/Tips/unix-w8.html


OpenLDAP Commands

Search ldap database:
view everything anonymously authenticated
ldapsearch -x -b 'dc=example,dc=com'
-x : unauthenticated
-b : baseDN
-h : host
-p : port (389 normal; 636 secure)

Same as above but more explicit
ldapsearch -x -b 'dc=example,dc=com' '(objectclass=*)'

The test in the parens can be used to restrict the search and return only records for which that test is true. For example, the following will only return the record whose uid is set to joeuser.
ldapsearch -x -b 'dc=example,dc=com' '(uid=joeuser)'

dm-crypt filesystem encryption

Dependencies needed:
Kernel Setup:
Device Drivers > Multi-device support (RAID and LVM) > Device Mapper Support (dm-mod)
Device Drivers > Multi-device support (RAID and LVM) > Crypt Target Support (dm-crypt)
Cryptographic Options > (Select cyphers .. ex. aes, twofish)

Userspace tools needed:
cryptsetup.sh
libdevmapper

cryptsetup.sh Syntax:

Syntax: cryptsetup [<OPTIONS>] <action> <name> [<device>]
  <OPTIONS>:
   -c <cipher> (see /proc/crypto)
   -h {plain/<hash>} (see hashalot)
   -y (verifies the passphrase by asking for it twice)
   -d <file> (read key from file
       e.g. /dev/urandom; useful for swap devices.
       If set, the parameters -h and -y will be ignored)
   -s <keysize> (in bits) (WARNING: in bytes for cryptsetup.sh)
   -b <size> (in sectors)
   -o <offset> (in sectors)
   -p <skipped> (in sectors)
   <action> is one of:
         create - create device
         remove - remove device
         reload - modify active device
         resize - resize active device
         status - show device status
   <name> is the device to create under /dev/mapper/
   <device> is the encrypted device

Create crypto physical device (sized by existing partition):
cryptsetup.sh -c aes -h plain -y -b `blockdev --getsize \
/dev/hdb2` create cryptvol1 /dev/hdb2

Copy over data:
dd if=/dev/hdb2 of=/dev/mapper/cryptvol1 bs=4k

http://www.linux.com/article.pl?sid=04/06/07/2036205
http://www.saout.de/misc/dm-crypt/

rsync

Syntax:

rsync -vaHx --progress --numeric-ids --delete \
--exclude-from=asylum_backup.excludes --delete-excluded \
username@host:/home/userdir/ /backupdir/

Common options:
-v: verbose
-r: recursive
-a: archive - maintain perms, ownership
-H: Maintain hard links
-x: no recursion into other filesystems
--progress: shows progress info
--numeric-ids: don't translate UID/GIDs; important for backups.
--delete: delete from backup files that no longer exist on server
--exclude-from=file.txt: specifies a file to exclude paths. One path per line.
--delete-excluded: delete files previous backup which are now within exclude list
username@: username on remote host
host:: name of host
/home/userdir: path to backup

    trailing slash: backup contents of dir
    no trailing slash: backup dir

/backupdir: location to backup files

Example of simple copy:
rsync -r -e ssh --delete /home/user/ user@host:/backups/


http://www.sanitarium.net/golug/rsync_backups.html
http://linuxgazette.net/104/odonovan.html

LVM Basics

Dependencies needed:
Kernel module (version 2.6.9+):
Device Drivers > Multi-device support (RAID and LVM) > Device Mapper Support (CONFIG_BLK_DEV_DM)
Associated kernel module:
dm_mod

Package:
lvm2 - lvm tools
libdevmapper

Show LVM version:
lvm version

Create the physical disks:
pvcreate /dev/hda
pvcreate /dev/hdb
pvcreate /dev/hdc1
pvcreate /dev/hdc2

Show allocated Physical volumes:
pvscan
pvdisplay
lvm pvs

Setup a volume group:
vgcreate vg_name /dev/hda /dev/hdb /dev/hdc1 /dev/hdc2

Display a volume group:
vgdisplay
lvm vgs

Display a logical volume:
lvdisplay
lvm lvs

Create Logical Volume:
Sets the size to 1GB
lvcreate -L1G -n lv_name vg_name

Activate/deactivate a volume group:
vgchange -a y vg_name #Activates: needed after each reboot!!
# This makes it show up as an entry in /dev/
vgchange -a n vg_name #Deactivates

Create the file system (choose one):
mk2fs /dev/vg_name/lv_name # create ext2 fs
mkfs.ext3 /dev/VolGroupBAK/lv_BAK # create ext2 fs
mkfs.ext3 /dev/VolGroupBAK/lv_BAK # create ext3 fs
mkreiserfs /dev/VolGroupBAK/lv_BAK # create reiserfs (reiserfs utils needed)
mkfs.xfs /dev/VolGroupBAK/lv_BAK # create xfs (xfsprogs package needed)
jfs_mkfs /dev/VolGroupBAK/lv_BAK # create jfs (jfsutils package needed)

Mount the File System:
mount /dev/vg_name/lv_name /mnt/point

Add disks to volume groups:
Create the new physical volumes
pvcreate /dev/hdd1
pvcreate /dev/hdd2

Add physical volumes to volume group
vgextend vg_name /dev/hdd1
vgextend vg_name /dev/hdd2

Unmount logical volume to extend
unmount /dev/vg_name/lv_name

Grow lv by 1GB
lvextend -L+1G /dev/vg_name/lv_name

Resize the underlying filesystem to fit (choose one)
resize2fs /dev/vg_name/lv_name # grow ext2/3 to match
resize_reiserfs -f /dev/vg_name/lv_name # grow reiserfs online
resize_reiserfs /dev/vg_name/lv_name # grow reiserfs offline
xfs_growfs /mount_pt # grow xfs online (must be mounted to resize)
mount -o remount,resize /home # grow jfs online (must be mounted)

Remount logical volume
mount /dev/vg_name/lv_name # remount if unmounted

Remove a Logical Volume:
unmount /dev/vg_name/lv_name # unmount any mounted lv
lvremove /dev/vg_name/lv_name # remove any lv

Remove a volume Group:
All logical volumes in group must be removed first.
vgchange -a n vg_name # deactivate vg
vgremove vg_name # removes vg

http://tldp.org/HOWTO/LVM-HOWTO/index.html
http://sources.redhat.com/lvm2/
http://www.die.net/doc/linux/man/man8/jfs_mkfs.8.html
http://www.die.net/doc/linux/man/man8/mkfs.xfs.8.html
http://www.howtoforge.com/linux_lvm_p2

httpd.conf Activate User Webspace

Load the User Directory module:
LoadModule userdir_module modules/mod_userdir.so

Add the following lines to activate user dirs:
<IfModule mod_userdir.c>
UserDir public_html #typical dir convention is public_html
</IfModule>

Set directory specific options (optional):
<Directory /export/home/*/public_html>
AllowOverride FileInfo AuthConfig Limit
Options MultiViews Indexes SymLinksIfOwnerMatch IncludesNoExec
<Limit GET POST OPTIONS>
Order allow,deny
Allow from all
</Limit>
<LimitExcept GET POST OPTIONS>
Order deny, allow
Deny from all
</LimitExcept>
</Directory>

Several Available Options:
All: all options except multiviews (default)
ExecCGI: Execution of CGI scripts is permitted
Indexes: if no DirectoryIndex (index.html) present in dir, display formated list
SymLinksIfOwnerMatch: follow sym links only if source and target owner match

Several Available AllowOverride directive settings:
This directive allows the use of .htaccess files to override
All: all options are allowed in .htaccess
AuthConfig: allow use of AuthName, AuthType, AuthUserFile, AuthGroupFile, Require, etc.
Indexes: allow use of DirectoryIndex and more
Limit: allow use of Allow, Deny and Order
Options: allow use of specific option settings (above)

http://httpd.apache.org/docs/1.3/mod/core.html#allowoverride

httpd.conf Basic Authentication.

Add these lines to a given directory section or .htaccess file:
AuthType Basic
AuthName "By Invitation Only"
AuthUserFile /etc/httpd/passwords
Require user admin1 admin2

Execute these commands to create / add users:
htpasswd -c /etc/httpd/passwords admin1 #create
htpasswd /etc/httpd/passwords rbowen admin2 #add

Or Create to stdout:
htpasswd -nbs user pass

To use a .htaccess file, the following is needed in a directory section:
AccessFileName .htaccess # ID .htaccess as override file (default)
AllowOverride AuthConfig # allows .htaccess to override authorization

http://httpd.apache.org/docs/1.3/howto/auth.html
http://httpd.apache.org/docs/1.3/mod/core.html#authname

Job Control

View the currently running jobs:
jobs

Place running foreground process into background:
ctl-z #puts the job to sleep
bg %1

Bring a background job into the foreground:
fg %1

Kill a job:
kill %1
kill %1 -9

Find the PID of all jobs
jobs -p
jobs -pl

Bring a nohuped process to the foreground
# note: I think you can only do this from the same terminal session.
# It doesn't look like it is possible to nohup a process, close a terminal
# and then bring the process back to the foreground again. Use screen instead.

# If you do not close your terminal session and if you do something like
nohup sleep 100 &
# and want to bring this to the foreground
# find the process ID using
jobs -p
or
ps -ef
# then supply the PID as the argument to the fg command
fg 14389420


http://www.gnu.org/software/bash/manual/html_node/Job-Control-Basics.html#Job-Control-Basics
http://www.uwyo.edu/askit/displaydoc.asp?askitdocid=262&parentid=1
http://linuxhelp.blogspot.com/2005/05/job-control-in-linux.html#axzz0gU42IqoP

Mencoder Usage

Listing available codecs:
mencoder -ovc help
mencoder -oac help

Basic encode syntax:
mencoder movie.wmv -o movie.avi -ovc lavc -oac lavc (mpeg4 default)
# -o = output file
# -ovc = output video codec
# -oac = output audio codec

One-pass FFmpeg (lavc) encoding:
mencoder file.avi -ovc lavc -oac lavc --ffourcc DX50 -o output.avi
mencoder file.avi -ovc lavc -oac lavc -lavaopts acodec=mp3 -o movie.avi

http://gentoo-wiki.com/HOWTO_Mencoder_Introduction_Guide

OpenSSL Usage

List available Ciphers:
openssl ciphers -v
openssl ciphers -v tls1 #only TLS 1 ciphers
openssl ciphers -v tls1.2 #only TLS 1.2 ciphers
openssl list-cypher-commands
openssl ciphers -v 'HIGH' #only good ciphers

Test OpenSSL Speed:
openssl speed
openssl speed rsa #test only rsa

Generate self-signed cert:
openssl req \
-x509 -nodes -days 365 \
-newkey rsa:1024 -keyout mycert.pem -out mycert.pem
OR
openssl req \
-x509 -nodes -days 365 \
-subj '/C=US/ST=Oregon/L=Portland/CN=www.madboa.com' \
-newkey rsa:1024 -keyout mycert.pem -out mycert.pem

MD5 or SHA1 digest of file:
openssl dgst -md5 filename
openssl dgst -sha1 filename

Base64 encode / decode a file:
openssl enc -base64 -in infile.txt #encode to stdout
openssl enc -base64 -in infile.txt -out outfile.txt #encode to a file
echo "encode me" | openssl enc -base64 #encode through a pipe
echo "Zw5jb2RlIGllCg==" | openssl enc -base64 -d #decode through a pipe

Encrypt a file using 256-bit AES in CBC mode
openssl enc -aes-256-cbc -salt -in file.txt -out file.enc
openssl enc -aes-256-cbc -salt -in file.txt \
-out file.enc -pass pass:password
openssl enc -aes-256-cbc -salt -in file.txt \
-out file.enc -pass file:/path/to/passwd.txt
openssl enc -aes-256-cbc -a -salt -in file.txt -out file.enc #base64 for email

Decrypt binary / base64 AES CBC file
openssl enc -d -aes-256-cbc -in file.enc
openssl enc -d -aes-256-cbc -a -in file.enc  # decode with base64

Encrypt a file using Triple DES with base64 "ASCII Armor"
openssl enc -e -a -salt -des3 -in file.txt -out file.des3

Decrypt a file encoded with Triple DES and base64 encoded
openssl enc -d -a -in file.des3 -out file.txt

Encrypt a file using Blowfish and base64 encode
openssl enc -e -a -salt -bf -in file.txt -out file.blowfish

Decrypt a file encoded with Blowfish and base64 encoded
openssl enc -d -a -bf -in file.blowfish -out file.txt

Generate an RSA key:
openssl genrsa
openssl genrsa -out mykep.pem 1024
openssl genrsa -des3 -out mykey.pem 1024

Generate a public RSA key:
openssl rsa -in mykey.pem -pubout

Generate a DES key:
openssl dsaparam -noout -out dsakey.pem -genkey 1024

Generate a shadow-style password hash:
openssl passwd -1 MySecret
openssl passwd -1 -salt sXiKzkus MySecret #specific salt

Test for prime number:
openssl prime 11905475924560753

Generate random number:
openssl rand -base64 128 #128 random base64 bits
openssl rand -out random_data.bin 1024 #1024 random binary bits
head -c 32 /dev/urandom | openssl enc -base64 #better entropy


Create an SSL certificate:
openssl genrsa -des3 -out server.key 1024            # create keys
openssl req -new -key server.key -out server.csr   # create cert request

cp server.key server.key.org                                  # remove passphrase
openssl rsa -in server.key.org -out server.key
openssl x509 -req -days 365 -in server.csr -signkey server.key -out server.crt  # create cert

Decode an SSL Cert:
openssl x509 -in certificate.crt -text -noout
http://www.sslshopper.com/certificate-decoder.html

Encrypt from STDIN to STDOUT with a simple AES password
echo "Plain Text" | openssl enc -aes-256-cbc -a

Decrypt from STDIN to STDOUT with a simple AES password 
echo "Cyphertext from above" | openssl enc -aes-256-cbc -d -a


http://www.akadia.com/services/ssh_test_certificate.html
http://www.yatblog.com/2007/02/27/how-to-create-a-ssl-certificate/
http://www.vanemery.com/Linux/Apache/openSSL.html
http://www.madboa.com/geek/openssl/

SSH PKI

To create ssh keys:
ssh-keygen -t dsa -d 2048
Optionally leave the passphrase blank
This will create a ~/.ssh/id_dsa and ~/.ssh/id_dsa.pub file.

Check for validity:
ssh-keygen -l -f ~/.ssh/id_dsa.pub

Copy the key to the remote server:
cat ~/.ssh/id_dsa ssh remote_host 'sh -c "cat - >>~/.ssh/authorized_keys"'

Convert commercial (SECSH) ssh private / public key to OpenSSH
ssh-keygen -i -f id_dsa.pub > id_dsa_openssh.pub # public key
ssh-keygen -i -f id_dsa > id_dsa_openssh # private key

Generate public key from private key
ssh-keygen -y -f id_dsa > id_dsa_openssh.pub

Convert OpenSSH private / public to commercial (SECSH) ssh
ssh-keygen -e -f id_dsa_openssh.pub > id_dsa.pub # public key
ssh-keygen -e -f id_dsa_openssh > id_dsa # private key

Changes the passphrase
ssh-keygen -p -N password -f id_dsa_openssh.prv > id_dsa

http://pkeck.myweb.uga.edu/ssh/
http://uaahosting.uaa.alaska.edu/axjww/sshkey/

GPG Management Commands

Generates key pair:
gpg --gen-key

Lists public and private current keys:
gpg --list-keys
gpg --list-secret-keys

Exports public key / private key:
gpg --armor --export jaz@example.com
gpg --export-secret-key --armor "jaz@example.com" > private.key

Imports a public key / private key:
gpg --import joe.ca
gpg --allow-secret-key-import --import private.key

Delete public / private key:
gpg --delete-key "jaz@example.com"
gpg --delete-secret-key "jaz@example.com"

Encrypt a document with someone's public key:
gpg --output out.gpg --encrypt --recipient jaz@example.com doc
gpg -o out.gpg -e -r jaz@example.com doc

Decrypt an encrypted file:
gpg --output doc --decrypt doc.pgp
gpg -o doc --decrypt doc.pgp

Symmetric encryption:
gpg --output doc.gpg --symmetric doc
gpg -o doc.gpg -c doc

Copy File Trees With Tar Pipes

Copy files on a local filesystem:
(cd /foo; tar -cf - . ) | (cd /bar; tar -xpf - )

Copy files on a remote filesystem:
(cd /src; tar -cvf - foo) | (ssh other.machine 'cd /dst; tar -xf -')


http://www.cs.hmc.edu/qref/targzip.html

Tar gzip and Bzip2 usage

Tar and bzip2 in one command:
tar -cf - /etc/ | bzip2 > etc.tar.bz2
tar -cjvf etc.tar.bz2 /etc/

Tar and gzip in one command:
tar -cvzf file.tar.gz files (GNU tar)
tar -cvf - files | gzip > file.tar.gz

List contents of gzip file:
gzcat file.tgz | tar -tvf -
gunzip < file.tgz | tar -tvf -

To Extract gzip (.tar.gz /.tgz) files:
gunzip < file.tgz | tar -xvf -
gzcat file.tgz | tar -xvf -
tar -zxvf file.tgz

List contents of bzip2 file:
bzcat jazwww.tar.bz2 | tar -tvf -
bzip2 -cd jazwww.tar.bz2 | tar -tvf -

To Extract bzip2 files:
bzcat jazwww.tar.bz2 | tar -xvf -
bzip2 -cd jazwww.tar.bz2 | tar -xvf -

To List or Extract a subset of files from a tar:
tar -tvf jazwww.tar usr/bin/
tar -xvf jazwww.tar usr/bin/
bzip2 -cd jazwww.tar.bz2 | tar -tvf - usr/bin/

# -p option preserves original permissions upon extract


http://en.wikipedia.org/wiki/Bzip2
http://www.gzip.org/

loopback mount

Enable loopback support in the kernel
Device Drivers > Block Devices > Loopback device support

Mount file / ISO
mount -o loop -t iso9660 filename.iso /mnt/iso

http://en.wikipedia.org/wiki/Loopback_mount