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Copy your ssh public key to a server from a machine that doesn't have ssh-copy-id

If you use Mac OS X or some other *nix variant that doesn't come with ssh-copy-id, this one-liner will allow you to add your public key to a remote machine so you can subsequently ssh to that machine without a password.
This is sample output - yours may be different.
70

cat ~/.ssh/id_rsa.pub | ssh user@machine "mkdir ~/.ssh; cat >> ~/.ssh/authorized_keys"

DEinspanjer · 2009-02-05 19:37:56 311
List files in an RPM package
This is sample output - yours may be different.
0

rpm --query --filesbypackage [packagename]

wwest4 · 2009-02-05 19:35:29 21
List RPM packages installed in current tree

shows all RPMs with files in the current directory & its subdirectories.
This is sample output - yours may be different.
0

find $PWD -exec rpm --query -f {} \; | sort -u | grep -v "not owned"

wwest4 · 2009-02-05 19:33:43 20
Periodic Log Deletion

deletes logs not modified in over [#] days - modify to compress or move, as needed
This is sample output - yours may be different.
1

find /path/to/dir -type f -mtime +[#] -exec rm -f {} \;

wwest4 · 2009-02-05 19:24:13 16
modify a file in place with perl

changes THIS to THAT in all files matching fileglob* without using secondary files
This is sample output - yours may be different.
2

perl -pi -e 's/THIS/THAT/g' fileglob*

elofland · 2009-02-05 19:19:52 60
Create a hard-to-guess password

Alternatively, if your password can contain a richer character set, try using 'uuencode' rather than base64. dd if=/dev/urandom bs=16 count=1 2>/dev/null | uuencode - Sample of that: '0:.CF\-@"\`W315VG^4O\.@``' Show Sample Output
This is sample output - yours may be different.
```
a5sXvbJx0pUY/CEuxwM4YA==
```
0

dd if=/dev/urandom bs=16 count=1 2>/dev/null | base64

twopoint718 · 2009-02-05 19:19:20 16
See whether your compiled Apache is prefork or worker MPM

For some of my web servers I setup and configure, for scaling I use the httpd.conf settings for these. Sometimes I forget which servers are prefork and which are worker MPM, so I use this to remind myself. Show Sample Output
This is sample output - yours may be different.
```
Compiled in modules:
  core.c
  prefork.c
  http_core.c
  mod_so.c
```
0

/usr/sbin/httpd -l

Mattie · 2009-02-05 19:06:43 57
Create a DOS floppy image

mount with: mount -t msdos -o loop ./floppy.img /tmp/mnt
This is sample output - yours may be different.
2

dd if=/dev/zero bs=1024 count=1440 > floppy.img && mkdosfs floppy.img

wwest4 · 2009-02-05 18:56:55 45
Print only the odd lines of a file
This is sample output - yours may be different.
-6

awk '{if (NR % 2 == 1) print $0}' file.txt

twopoint718 · 2009-02-05 18:43:19 24
Print only the even lines of a file
This is sample output - yours may be different.
-4

awk '{if (NR % 2 == 0) print $0}' file.txt

twopoint718 · 2009-02-05 18:41:38 32
Test for Weak SSL Ciphers

...if you get a certificate back, the server is accepting weak SSL ciphers
This is sample output - yours may be different.
6

openssl s_client -connect [host]:[sslport] -cipher LOW

wwest4 · 2009-02-05 18:37:50 38
Translate your terminal into Swedish Chef

Bork, bork, bork! To keep it short, the first terminal line doesn't show a prompt. Show Sample Output
This is sample output - yours may be different.
```
bork@bork:$ ps
  bork bork          bork bork
10640 bork/0    00:00:03 bork
12467 bork/0    00:00:00 bork
12469 bork/0    00:00:00 bork
12470 bork/0    00:00:00 bork
bork@bork:$ pwd 
/bork/bork/bork
bork@bork:$ whoami
bork
bork@bork:$
```
3

perl -e '$b="bork"; while(<STDIN>){$l=`$_ 2>&1`; $l=~s/[A-Za-z]+/$b/g; print "$l$b\@$b:\$ ";}'

fonik · 2009-02-05 18:33:40 28
Update twitter via curl
This is sample output - yours may be different.
166

curl -u user:pass -d status="Tweeting from the shell" http://twitter.com/statuses/update.xml

adamm9 · 2009-02-05 18:33:23 68
Rotate the X screen via xrandr

You need the RANDR support enable, to enable it with an ATI card run: aticonfig --set-pcs-str="DDX,EnableRandr12,TRUE" To show your available output run: xrandr -q -d [yourdisplay]
This is sample output - yours may be different.
0

xrandr --output [youroutput] --rotate [right|left|normal] -d [yourdisplay]

michelem · 2009-02-05 18:28:43 29
In-Place search/replace with datestamped backup

Does an in situ search-replace but leaves a datestamped backup. A variation with more precision: sed -i.`date +%Y%m%d%H%M%S 's/pattern/replace' [filename]
This is sample output - yours may be different.
1

sed -i.`date +%Y%m%d` -e 's/pattern/replace' [filename]

wwest4 · 2009-02-05 18:20:54 31
watch process stack, sampled at 1s intervals

This command repeatedly gets the specified process' stack using pstack (which is an insanely clever and tiny wrapper for gdb) and displays it fullscreen. Since it updates every second, you rapidly get an idea of where your program is stuck or spending time. The 'tac' is used to make the output grow down, which makes it less jumpy. If the output is too big for your screen, you can always leave the 'tac' off to see the inner calls. (Or, better yet--get a bigger screen.) Caveats: Won't work with stripped binaries and probably not well with threads, but you don't want to strip your binaries or use threads anyway. Show Sample Output
This is sample output - yours may be different.
```
Every 1.0s: pstack 2558 | tac                      Thu Feb  5 12:04:57 2009

#24 0x00000030fea1d8b4 in __libc_start_main () from /lib64/libc.so.6
#23 0x0000000000412275 in Py_Main ()
#22 0x00000000004a86e0 in PyRun_SimpleFileExFlags ()
#21 0x00000000004a844e in PyRun_FileExFlags ()
#20 0x00000000004872a2 in PyEval_EvalCode ()
...
#3  0x00002b2368b40a3f in search_peptide () from /n/site/inst/Linux-x86_64/bioi
#2  0x00002b2368b405f8 in choose_residue_mod ()
#1  0x00002b2368b3ff86 in evaluate_peptide () from /n/site/inst/Linux-x86_64/bi
#0  0x00002b2368b3f181 in score_spectrum () from /n/site/inst/Linux-x86_64/bioi
```
8

watch -n 1 'pstack 12345 | tac'

mkc · 2009-02-05 18:17:00 29
Change every instance of OLD to NEW in file FILE

Very quick way to change a word in a file. I use it all the time to change variable names in my PHP scripts (sed -i 's/$oldvar/$newvar/g' index.php)
This is sample output - yours may be different.
4

sed -i 's/OLD/NEW/g' FILE

nanexcool · 2009-02-05 18:07:41 26
Customizable Search Context

customizable context searches - if you know sed, this is a basis for more complex context control than grep --context offers Show Sample Output
This is sample output - yours may be different.
```
$ echo -n search\>\  ; read SEARCH_STRING && sed -n "/$SEARCH_STRING/{n;p;n;p;n;p;q}" /etc/passwd
search> sshd
suse-ncc:x:105:107:Novell Customer Center User:/var/lib/YaST2/suse-ncc-fakehome:/bin/bash
uucp:x:10:14:Unix-to-Unix CoPy system:/etc/uucp:/bin/bash
uuidd:x:100:101:User for uuidd:/var/run/uuidd:/bin/false
```
0

echo -n search\>\ ; read SEARCH_STRING && sed -n "/$SEARCH_STRING/{n;p;n;p;n;p;q}" [file-to-search]

wwest4 · 2009-02-05 18:07:23 28

Shows a tree view of parent to child processes in the output of ps (linux). Similar output can be achieved with pstree (also linux) or ptree (Solaris). Show Sample Output

ps auxf

systemj · 2009-02-05 18:07:16 18

List the number and type of active network connections
This is sample output - yours may be different.
26

netstat -ant | awk '{print $NF}' | grep -v '[a-z]' | sort | uniq -c

himynameisthor · 2009-02-05 18:02:59 36
Unrar multiple directories into current working directory

Grabs all rar files in any current subdirectories and feeds it to unrar. Doesn't work well with things packaged like file.part01.rar. Works best with File.rar. You can recurse into other directories by adding more /*'s
This is sample output - yours may be different.
2

for x in */*.rar; do unrar x $x; done

sheptard · 2009-02-05 18:01:58 18
Export a subset of a database

Limits the number of rows per table to X
This is sample output - yours may be different.
1

mysqldump --where="true LIMIT X" databasename > output.sql

bradbeattie · 2009-02-05 17:57:32 60
Extract raw URLs from a file
This is sample output - yours may be different.
-1

egrep -ie "<*HREF=(.*?)>" index.html | awk -F\" '{print $2}' | grep ://

wwest4 · 2009-02-05 17:51:14 22
Display any tcp connections to apache

Sometimes apache will get stuck in an established state where you can't get a list of the connecting IP's from mod_status... not a good thing when you need to ban an abusive ip.
This is sample output - yours may be different.
6

for i in `ps aux | grep httpd | awk '{print $2}'`; do lsof -n -p $i | grep ESTABLISHED; done;

Shadow · 2009-02-05 17:50:52 67
Recursively remove .svn directories from the current location
This is sample output - yours may be different.
16

find . -type d -name '.svn' -print0 | xargs -0 rm -rdf

blue64 · 2009-02-05 17:47:03 31
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Show Directories in the PATH Which does NOT Exist

Tells you where a command is in your $PATH, but also wether it's a link and to what.

You may also use the $(which foo) variant instead of backticks. I personnaly have an alias ll='ls -l'.

Does a full update and cleaning in one line

Run bash on top of a vi session (saved or not saved), run multiple commands, instead of one at a time with :!(bashcommand), type exit and [enter] to get back to where you left off in vi.

Display a block of text with AWK

I find this terribly useful for grepping through a file, looking for just a block of text. There's "grep -A # pattern file.txt" to see a specific number of lines following your pattern, but what if you want to see the whole block? Say, the output of "dmidecode" (as root): $ dmidecode | awk '/Battery/,/^$/' Will show me everything following the battery block up to the next block of text. Again, I find this extremely useful when I want to see whole blocks of text based on a pattern, and I don't care to see the rest of the data in output. This could be used against the '/etc/securetty/user' file on Unix to find the block of a specific user. It could be used against VirtualHosts or Directories on Apache to find specific definitions. The scenarios go on for any text formatted in a block fashion. Very handy.

attach to bash shell in the last container you started

Quickly ping range of IP adresses and return only those that are online

Connect via sftp to a specific port

I use this for connect via sftp to a server listening on a non default ssh port.

Calculate days on which Friday the 13th occurs (inspired from the work of the user justsomeguy)

Friday is the 5th day of the week, monday is the 1st. Output may be affected by locale.

Compress and store the image of a disk over the network

Create an image of "device" and send it to another machine through the network ("target" and "port" sets the ip and port the stream will be sent to), outputting a progress bar On the machine that will receive, compress and store the file, use: $nc -l -p | 7z a -si -m0=lzma2 -mx=9 -ms=on Optionally, add the -v4g switch at the end of the line in order to split the file every 4 gigabytes (or set another size: accepted suffixes are k, m and g). The file will be compressed using 7z format, lzma2 algorithm, with maximum compression level and solid file activated. The compression stage will be executed on the machine which will store the image. It was planned this way because the processor on that machine was faster, and being on a gigabit network, transfering the uncompressed image wasn't much of a problem.

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