2012-02-26T01:15:25Z

Duncan:

At work I needed access to CentOS's vault site (http://vault.centos.org) from an internal network without outside access. I set a list of requirements for this task:

* Everything should be cached to accelerate subsequent pulls
* I should be able to hit a web server without specifying a port
* I wanted to minimize total caches I had to manage

Since I already had a working Squid & Apache installation, I used those.

=Squid Configuration=

I wanted to have Squid use a total of 5GB of space and only cache objects < 500MB in size. Season to taste.

cache_dir ufs /var/spool/squid 5120 16 256
maximum_object_size 512000 KB

Now I need to tell Squid to proxy to vault.centos.org on local port 8080

http_port 127.0.0.1:8080 accel defaultsite=vault.centos.org

Now we'll set expiration policies. Keep RPMs around, quickly expire repository data.

# keep RPMs for 7-10 days, keep repository data for 5-30 minutes
refresh_pattern \.rpm$ 10080 100% 14400
refresh_pattern repodata 5 50% 30

There's probably a better way to do this involving ACLs, but I just use a blanket statement. Put this at the end of the config file.

always_direct allow all

Now you'll want to restart squid.

=Apache Configuration=

You'll need to properly configure VirtualHosts in Apache. This is as simple as adding the following to /etc/httpd/conf/httpd.conf

NameVirtualHost *:80

I saved this as '''/etc/httpd/conf.d/vault.conf''' since Apache 2 in RHEL has an include against conf.d/*.conf. This a very simple VirtualHost that takes advantage of ProxyPass & ProxyPassReverse. The trailing slash is extremely important.

<VirtualHost *:80>
ServerName vault.duncanbrown.org
ServerAlias vault.duncanbrown.org
ErrorLog /var/www/vault/logs/error_log
CustomLog /var/www/vault/logs/access_log common

ProxyPass / http://localhost:8080/
ProxyPassReverse / http://localhost:8080/
</VirtualHost>

Now you'll want to restart Apache.

=Finishing Up=

Once your DNS is configured properly & your domain name resolves everything should work.

2011-07-18T19:24:33Z

Duncan: /* Regions */

GNU Screen is one of the most useful pieces of software I've ever come across. It allows you to keep a terminal up and running that you're able to re-connect to remotely, share a terminal with another user, split your terminal into sections & much more.

Apparently there's discussion as to what exactly screen is. Is it a terminal multiplexer? Is it a window manager? I guess it really depends on where you're standing. People who are using [http://en.wikipedia.org/wiki/GNOME GNOME], [http://en.wikipedia.org/wiki/Kde KDE], [http://en.wikipedia.org/wiki/Mac_os_x Mac OS X], [http://en.wikipedia.org/wiki/Windows Windows] or any other environment where you run a [http://en.wikipedia.org/wiki/Terminal_emulator Terminal Emulator] then it's more of a multiplexer. If you're just running a machine without a window manager, then I guess screen IS your window manager.

But whatever.

=Configuration=

Configuring screen can be an incredibly tedious process involving hours and hours of reading documentation, or you can just search the web for someone else's .screenrc... like mine.

==My .screenrc==

My .screenrc can be downloaded at http://files.duncanbrown.org/linux/dotfiles/.screenrc

Here is a screen capture of what my current screen session looks like :

[[Image:Screen_Screenshot.png]]

The weather information and current [http://en.wikipedia.org/wiki/Load_(computing) Load Average] are collected by something other than screen, you can find that information on how it works at http://files.duncanbrown.org/linux/dotfiles

==Set The Status Line To Something Useful==

Add this to your .bashrc or .bash_profile

case $TERM in
*screen*) export PROMPT_COMMAND='echo -ne "\033]0;${USER}@${HOSTNAME%%.*}:${PWD/#$HOME/~}\007"'
;;
esac

=Multi-User Mode=

'''This is ripped directly from Gentoo's site, I need to clean it up so it's not a direct plagiary.'''

http://gentoo-wiki.com/HOWTO_Snoop_terminal_session#Screen

Using [[Screen]] in multiuser mode requires screen to be as setuid root. If you know about the potential security implications you can enable it by issuing
# chmod u+s `which screen`

We need to configure screen to use multiuser mode and change privileges for the guest.
Put the following commands into ~/.screenrc. You can also use them in a screen session after pressing '''^A'''

multiuser on
aclchg snoopy -x "?" #Revoke permission to execute any screen command
aclchg snoopy +x "wall" #Allow writing simple messages in the terminal status line
aclumask snoopy-wx #Default permissions to windows
acladd snoopy #Enable user snoopy to access screen session

Start screen:
user@localhost $ screen

user@localhost $ screen -ls
There is a screen on:
11521.pts-4.hostname (Multi, attached)
1 Socket in /var/run/screen/S-user.

Now the guest can attach to the screen:

snoopy@localhost $ screen -r user/11521

=Using Screen=

In this section you'll see letters prefaced with '''^''', this translates into CTRL-X.

==Basic Commands==

{|
| '''^A ?'''
| Help.
|-
| '''^A a'''
| Send the command character itself ("^a") to the program running in the current window.
|-
| '''^A t'''
| Show time, date, hostname, and some other stuff.
|-
| '''^A @'''
| Do nothing. (Useful when you hit "^a" by mistake.)
|-
| '''^A :'''
| Enter command line mode. (For example, "^a :number 7" changes the window number of the current window to 7. See the man page for more details.)
|-
| '''^A ^Z'''
| Suspend screen. (You will be back at the shell you started screen from.)
|-
| '''^A d'''
| Detach screen. (Do this before you log out -- you will be back at the shell you started screen from.)
|}

==Window Navigation & Management==

{|
| '''^A ^A'''
| Switch to the last used window
|-
| '''^A ^N'''
| Switch to the next window
|-
| '''^A ^P'''
| Switch to the previous window
|-
| '''^A 0'''
| Switch to window number 0 (works with 0-9).
|-
| '''^A "'''
| Present a list of all windows for selection. Use the arrow or number keys (or vi- or Emacs-style cursor keys) to highlight a window and press <Enter> to switch to it.
|-
| '''^A c'''
| Create a new window with a shell and switch to that window
|-
| '''^A A'''
| Change the current window's title
|-
| '''^A ''''
| Prompt for a window name/number to switch to
|-
| '''^A F'''
| Resize the window to the current region size
|-
| '''^A K'''
| Kill the current window
|-
| '''^A l'''
| Refresh current window
|-
| '''^A i'''
| Show information on the current window
|-
| '''^A N'''
| Show name & number of current window
|-
| ''''''
|
|}

==Copy/Scrollback Mode==

{|
| '''^A ['''
| Enter scrollback mode
|-
| '''^A ]'''
| Send the contents of the paste buffer to the program running in the current window
|-
| '''h,j,k,l'''
| Move cursor left, down, up, right (as in vi/vim). Regular arrow keys also work.
|-
| '''^B'''
| Page up (<PageUp> key also works).
|-
| '''^F'''
| Page down (<PageDown> key also works).
|-
| '''<Space>'''
| Set mark. When the second mark is set, the text between the two marks will be put into screen's paste buffer and copy/scrollback mode will be exited.
|-
| '''^'''
| Move to first nonwhitespace character on current line.
|-
| '''$'''
| Move to last nonwhitespace character on current line.
|-
| '''0'''
| Move to leftmost column.
|-
| '''c'''
| Set the left margin for block-mode copying.
|-
| '''C'''
| Set the right margin for block-mode copying.
|-
| '''x'''
| Exchange the first mark with the current cursor position. This is good for moving an already set mark.
|-
| '''<Esc>'''
| Exit copy/scrollback mode. (Any key that doesn't have another meaning will do this.)
|}

[[Image:Split Screen.png|right|thumb|A split screen featuring [[Mac OS X]] on top & [[GNU/Linux]] on the bottom]]
Regions allow looking at two or more screen windows at the same time.

==Regions==

{|
| '''^A S'''
| Split the current region horizontally.
|-
| '''^A |'''
| Split the current region vertically.
|-
| '''^A ^I'''
| Switch focus to the next region.
|-
| '''^A Q'''
| Delete all regions but the current one. (This does not destroy any windows.)
|}

I need to integrate the info from http://www.mail-archive.com/screen-users@gnu.org/msg01032.html

=Logging=

{|
|-
| '''^A h'''
| Write a hardcopy of current window to '''hardcopy.N'''
|-
| '''^A H'''
| Toggles logging of current window to '''screenlog.N'''
|-
| ''''''
|
|-
| ''''''
|
|-
| ''''''
|
|-
| ''''''
|
|}

=Misc=

{|
|-
| '''^A '''
|
|-
| ''''''
|
|-
| ''''''
|
|-
| ''''''
|
|-
| ''''''
|
|}

=More Stuff=

I've found that GNU Screen can be even more useful when you rotate your X11 display by 90 degrees! A split screen gives you much more usable real estate than a standard horizontal monitor. If you're interested, check out [[Rotating X.org Screens]].

GNU Screen

2011-07-18T19:23:09Z

Duncan:

GNU Screen is one of the most useful pieces of software I've ever come across. It allows you to keep a terminal up and running that you're able to re-connect to remotely, share a terminal with another user, split your terminal into sections & much more.

Apparently there's discussion as to what exactly screen is. Is it a terminal multiplexer? Is it a window manager? I guess it really depends on where you're standing. People who are using [http://en.wikipedia.org/wiki/GNOME GNOME], [http://en.wikipedia.org/wiki/Kde KDE], [http://en.wikipedia.org/wiki/Mac_os_x Mac OS X], [http://en.wikipedia.org/wiki/Windows Windows] or any other environment where you run a [http://en.wikipedia.org/wiki/Terminal_emulator Terminal Emulator] then it's more of a multiplexer. If you're just running a machine without a window manager, then I guess screen IS your window manager.

But whatever.

=Configuration=

Configuring screen can be an incredibly tedious process involving hours and hours of reading documentation, or you can just search the web for someone else's .screenrc... like mine.

==My .screenrc==

My .screenrc can be downloaded at http://files.duncanbrown.org/linux/dotfiles/.screenrc

Here is a screen capture of what my current screen session looks like :

[[Image:Screen_Screenshot.png]]

The weather information and current [http://en.wikipedia.org/wiki/Load_(computing) Load Average] are collected by something other than screen, you can find that information on how it works at http://files.duncanbrown.org/linux/dotfiles

==Set The Status Line To Something Useful==

Add this to your .bashrc or .bash_profile

case $TERM in
*screen*) export PROMPT_COMMAND='echo -ne "\033]0;${USER}@${HOSTNAME%%.*}:${PWD/#$HOME/~}\007"'
;;
esac

=Multi-User Mode=

'''This is ripped directly from Gentoo's site, I need to clean it up so it's not a direct plagiary.'''

http://gentoo-wiki.com/HOWTO_Snoop_terminal_session#Screen

Using [[Screen]] in multiuser mode requires screen to be as setuid root. If you know about the potential security implications you can enable it by issuing
# chmod u+s `which screen`

We need to configure screen to use multiuser mode and change privileges for the guest.
Put the following commands into ~/.screenrc. You can also use them in a screen session after pressing '''^A'''

multiuser on
aclchg snoopy -x "?" #Revoke permission to execute any screen command
aclchg snoopy +x "wall" #Allow writing simple messages in the terminal status line
aclumask snoopy-wx #Default permissions to windows
acladd snoopy #Enable user snoopy to access screen session

Start screen:
user@localhost $ screen

user@localhost $ screen -ls
There is a screen on:
11521.pts-4.hostname (Multi, attached)
1 Socket in /var/run/screen/S-user.

Now the guest can attach to the screen:

snoopy@localhost $ screen -r user/11521

=Using Screen=

In this section you'll see letters prefaced with '''^''', this translates into CTRL-X.

==Basic Commands==

{|
| '''^A ?'''
| Help.
|-
| '''^A a'''
| Send the command character itself ("^a") to the program running in the current window.
|-
| '''^A t'''
| Show time, date, hostname, and some other stuff.
|-
| '''^A @'''
| Do nothing. (Useful when you hit "^a" by mistake.)
|-
| '''^A :'''
| Enter command line mode. (For example, "^a :number 7" changes the window number of the current window to 7. See the man page for more details.)
|-
| '''^A ^Z'''
| Suspend screen. (You will be back at the shell you started screen from.)
|-
| '''^A d'''
| Detach screen. (Do this before you log out -- you will be back at the shell you started screen from.)
|}

==Window Navigation & Management==

{|
| '''^A ^A'''
| Switch to the last used window
|-
| '''^A ^N'''
| Switch to the next window
|-
| '''^A ^P'''
| Switch to the previous window
|-
| '''^A 0'''
| Switch to window number 0 (works with 0-9).
|-
| '''^A "'''
| Present a list of all windows for selection. Use the arrow or number keys (or vi- or Emacs-style cursor keys) to highlight a window and press <Enter> to switch to it.
|-
| '''^A c'''
| Create a new window with a shell and switch to that window
|-
| '''^A A'''
| Change the current window's title
|-
| '''^A ''''
| Prompt for a window name/number to switch to
|-
| '''^A F'''
| Resize the window to the current region size
|-
| '''^A K'''
| Kill the current window
|-
| '''^A l'''
| Refresh current window
|-
| '''^A i'''
| Show information on the current window
|-
| '''^A N'''
| Show name & number of current window
|-
| ''''''
|
|}

==Copy/Scrollback Mode==

{|
| '''^A ['''
| Enter scrollback mode
|-
| '''^A ]'''
| Send the contents of the paste buffer to the program running in the current window
|-
| '''h,j,k,l'''
| Move cursor left, down, up, right (as in vi/vim). Regular arrow keys also work.
|-
| '''^B'''
| Page up (<PageUp> key also works).
|-
| '''^F'''
| Page down (<PageDown> key also works).
|-
| '''<Space>'''
| Set mark. When the second mark is set, the text between the two marks will be put into screen's paste buffer and copy/scrollback mode will be exited.
|-
| '''^'''
| Move to first nonwhitespace character on current line.
|-
| '''$'''
| Move to last nonwhitespace character on current line.
|-
| '''0'''
| Move to leftmost column.
|-
| '''c'''
| Set the left margin for block-mode copying.
|-
| '''C'''
| Set the right margin for block-mode copying.
|-
| '''x'''
| Exchange the first mark with the current cursor position. This is good for moving an already set mark.
|-
| '''<Esc>'''
| Exit copy/scrollback mode. (Any key that doesn't have another meaning will do this.)
|}

[[Image:Split Screen.png|right|thumb|A split screen featuring [[Mac OS X]] on top & [[GNU/Linux]] on the bottom]]
Regions allow looking at two or more screen windows at the same time.

==Regions==

{|
| '''^A S'''
| Split the current region horizontally.
|-
| '''^A |'''
| Split the current region vertically.
|-
| '''^A ^I'''
| Switch focus to the next region.
|-
| '''^A Q'''
| Delete all regions but the current one. (This does not destroy any windows.)
|}

=Logging=

{|
|-
| '''^A h'''
| Write a hardcopy of current window to '''hardcopy.N'''
|-
| '''^A H'''
| Toggles logging of current window to '''screenlog.N'''
|-
| ''''''
|
|-
| ''''''
|
|-
| ''''''
|
|-
| ''''''
|
|}

=Misc=

{|
|-
| '''^A '''
|
|-
| ''''''
|
|-
| ''''''
|
|-
| ''''''
|
|-
| ''''''
|
|}

=More Stuff=

I've found that GNU Screen can be even more useful when you rotate your X11 display by 90 degrees! A split screen gives you much more usable real estate than a standard horizontal monitor. If you're interested, check out [[Rotating X.org Screens]].