Greg Back

macOS Keyboard Symbols

2021-06-26T15:26:00-04:00

A handy reference for myself for every time I forget these

Symbol	Key
⌘	Command
^	Control
⌥	Option
⇧	Shift

Homebrew `depends_on` errors

2021-06-26T15:08:00-04:00

If you're trying to install (or more likely uninstall) an old Homebrew Cask, you might get an error like:

Error: Cask 'spectacle' definition is invalid: invalid 'depends_on macos' value: unknown or unsupported macOS version: :lion

To fix this, you can run the following command to "fix" the manifests of all currently-installed Casks:

/usr/bin/find "$(brew --prefix)/Caskroom/"*'/.metadata' -type f -name '*.rb' -print0 | /usr/bin/xargs -0 /usr/bin/perl -i -pe 's/depends_on macos: \[.*?\]//gsm;s/depends_on macos: .*//g'

Source: Homebrew/homebrew-cask#58046

The `-o` option to `grep`

2021-04-11T19:18:00-04:00

I don't know how I made it this long in my technical career without knowing about the -o option to grep, which prints only the part of the line that matches the regular expression, not the entire line. I have spent way too much time post-processing the results with sed, awk, etc. (and learned a lot in the process), but hopefully this will save me (and you) some time in the future.

Source: grep(1) man page

Exploring Sqlite databases

2021-03-28T23:15:00-04:00

It's often useful to peek around a sqlite database file from the command line, especially those that applications use for storing their own internal data. In this case, I was interested in looking at how Firefox stores a user's browsing history (which happens to be in the file called places.sqlite inside the Firefox profile directory). Anyway, here are some commands you can run:

$ sqlite places.sqlite
sqlite> .help
sqlite> .tables
sqlite> .dbinfo
sqlite> PRAGMA table_info(moz_places)
sqlite> .quit

moz_places is the name of the specific table I was interested in.

Rebase warning when running `brew update`

2021-03-19T23:03:00-04:00

If you run brew update and see output that looks like this:

fatal: It seems that there is already a rebase-merge directory, and
I wonder if you are in the middle of another rebase.  If that is the
case, please try
        git rebase (--continue | --abort | --skip)
If that is not the case, please
        rm -fr ".git/rebase-merge"
and run me again.  I am stopping in case you still have something
valuable there.

Already up-to-date.

You can fix it by running brew update-reset.

This happened to me today and I spent way too long looking for the solution.

[Source: GitHub comment by @joshuapinter]

The `date` command

2021-03-19T22:43:00-04:00

The Linux date command can be used to get the current date (and also to modify the date of your machine, but I've never used it for that). It's useful if you want to programmatically add a date to a filename, either one time or as part of a regularly-scheduled or repeated task.

Here are some of the frequently used formats I use:

Command	Sample Output	Notes
`date +%F`	`2021-03-19`	If you just need the date
`date +"%F %R"`	`2021-03-19 22:43`	Like the date and time of this post
`date +"%Y-%m-%dT%H:%M:%S%z"`	`2021-03-19T22:43:52-0400`	ISO 8601 time in the local time zone.
`date -Iseconds`	`2021-03-19T22:43:52-04:00`	Same, except including a ":" in the offset (does not work on macOS)
`date -u +"%Y-%m-%dT%H:%M:%S%z"`	`2021-03-20T02:43:52+0000`	ISO 8601 date in UTC
`date -u +"%Y-%m-%dT%H:%M:%SZ"`	`2021-03-20T02:43:52Z`	Same, but using `Z` instead of `+0000`
`date -u -Iseconds`	`2021-03-20T02:51:58+00:00`	Same with colon in the output (does not work on macOS)

For more information, see this Stack Exchange post or the date man page (along with the strftime man page for formatting options).

Careful with those Backslashes!

2018-06-21T10:59:00-04:00

Brainteaser of the day

Given a MySQL database, what value will be put in the database for each of the following Python statements?

# normal string, 4 backslashes
db.execute( "INSERT INTO `test` (`text`) VALUES ('x\\\\y');")
# raw string, 2 backslashes
db.execute(r"INSERT INTO `test` (`text`) VALUES ('x\\y');"  )
# normal string, 3 backslashes
db.execute( "INSERT INTO `test` (`text`) VALUES ('x\\\y');" )
# raw string, 3 backslashes
db.execute(r"INSERT INTO `test` (`text`) VALUES ('x\\\y');" )

Take a guess, or try it out before looking at the answer below. If you want to set up a database yourself, the following snippets should help.

Code to set up a database and table

from sqlalchemy import create_engine engine = create_engine('mysql://root@localhost/') db = engine.connect() db.execute(""" DROP DATABASE IF EXISTS test_db; CREATE DATABASE test_db; USE test_db; CREATE TABLE `test` ( `id` int(11) NOT NULL AUTO_INCREMENT, `text` char(8) NOT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8mb4;""" ) db.close()

Code to dump contents of database

from sqlalchemy import create_engine engine = create_engine('mysql://root@localhost/test_db') db = engine.connect() # Put insert commands here. res = db.execute("""SELECT text FROM test;""").fetchall() for row in res: print(row) db.close()

Here are some adorable Basset Hound pictures for you to look at before scrolling down to see the answer.

Answer

All four will result in the same data being in the database:

x\y
x\y
x\y
x\y

Crazy, huh!?

I was confused too until I looked a bit more at the documentation and did some experimentation.

Backslashes in Python

Backslashes in Python string literals sometimes need to be escaped.

print('a\\a')      # => a\a
print('a\a')       # => a (\a is the escape for BEL)
print('a\s')       # => a\s (\s is not a valid escape, so Python assumes the backslash is literal - DANGER!)
print('a\\s')      # => a\s
'a\\s' == 'a\s'    # True

Unlike Standard C, all unrecognized escape sequences are left in the string unchanged, i.e., the backslash is left in the result. (This behavior is useful when debugging: if an escape sequence is mistyped, the resulting output is more easily recognized as broken.) It is also important to note that the escape sequences only recognized in string literals fall into the category of unrecognized escapes for bytes literals.

Python 3 documentation (and similar for Python 2)

This is part of the reason that "raw" string literals (prefixed with 'r') are useful:

print(r'a\\a')     # => a\\a
print(r'a\a')      # => a\a
print(r'a\s')      # => a\s
print(r'a\\s')     # => a\\s
r'a\\s' == r'a\s'  # False

Backslashes in MySQL

MySQL similarly uses backslash as an escape. However, differently from Python, if a backslash is not part of a recognized escape sequence, the backlash is just dropped.

INSERT INTO `test` (`text`) VALUES ('a\\a');  -- a\a
INSERT INTO `test` (`text`) VALUES ('a\aa');  -- aaa
INSERT INTO `test` (`text`) VALUES ('a\ta');  -- a  a (literal tab character between two a's)
INSERT INTO `test` (`text`) VALUES ('a\a');   -- aa

MySQL recognizes the escape sequences shown in Table 9.1, "Special Character Escape Sequences". For all other escape sequences, backslash is ignored. That is, the escaped character is interpreted as if it was not escaped. For example, \x is just x. These sequences are case-sensitive. For example, \b is interpreted as a backspace, but \B is interpreted as B.

MySQL 5.7 documentation

Putting it together

This combination leads to confusing results. So in the example below (different than the four original statements):

db.execute("""INSERT INTO `test` (`text`) VALUES ('x\\y');""")

This is not using a raw string, so the actual command passed to SQL is:

INSERT INTO `test` (`text`) VALUES ('x\y');

Since \y is not a valid escape sequence for MySQL, the table just contains xy.

Both of the following (the first two examples at the top) will insert x\y:

db.execute( "INSERT INTO `test` (`text`) VALUES ('x\\\\y');")
db.execute(r"INSERT INTO `test` (`text`) VALUES ('x\\y');")

because the SQL command in both cases is:

INSERT INTO `test` (`text`) VALUES ('x\\y')

Confusingly, the other two examples also both result in the same data in the database, but for vastly different reasons:

db.execute( "INSERT INTO `test` (`text`) VALUES ('x\\\y');")

In this case, it's because Python will see the first two backslashes as a single properly-escaped backslash, but also leave the third backslash in, resulting in the same SQL command as the first two examples.

The last example is perhaps the most confusing, because it generates a different SQL command:

db.execute(r"INSERT INTO `test` (`text`) VALUES ('x\\\y');")

INSERT INTO `test` (`text`) VALUES ('x\\\y');

In this case, MySQL treats the first two backslashes as a single properly-escaped backslash, but then "drops" the third one, so the resulting data in the table is still x\y.

Go forth and be careful with those backslashes!

Image credits

By Anderson Nascimento [CC BY 2.0], via Wikimedia Commons
By eda [Public domain], from Wikimedia Commons

ssh-keygen

2014-08-01T19:27:00-04:00

I always forget the exact syntax and options I need for this. I don't create new keys frequently enough to remember without looking up what to run each time.

The command

ssh-keygen -t rsa -b 2048

[Source: Security StackExchange]

Run Wireshark as non-root user

2014-03-04T11:46:00-05:00

I frequently get frustrated when Wireshark won't run as a non-root user due to permissions on the dumpcap process. Here's the fix:

sudo groupadd wireshark
sudo usermod -a -G wireshark $USER
sudo chgrp wireshark /usr/bin/dumpcap
sudo chmod 754 /usr/bin/dumpcap
sudo setcap 'CAP_NET_RAW+eip CAP_NET_ADMIN+eip' /usr/bin/dumpcap
exec su -l $USER  # reload groups for user

Alternatively, you can log out and log back in to refresh the groups the user is in.

Ubuntu Default Folders

2013-03-24T00:39:00-04:00

I recently switched my primary machine from Windows 7 to Ubuntu. I'd always used an Ubuntu VM for development. Now I just have a Windows 7 VM for Windows-only applications, and do the majority of my work in Ubuntu. I'm fairly comfortable on the command line, but extremely dislike capital letters in file paths. So the Ubuntu defaults ("Documents", "Downloads", etc.) just weren't doing it for me. Fortunately, I found a blog post which explained which file sets these names ($HOME/.config/user-dirs.dirs).

My complete configuration is shown below.

# This file is written by xdg-user-dirs-update
# If you want to change or add directories, just edit the line you're
# interested in. All local changes will be retained on the next run
# Format is XDG_xxx_DIR="$HOME/yyy", where yyy is a shell-escaped
# homedir-relative path, or XDG_xxx_DIR="/yyy", where /yyy is an
# absolute path. No other format is supported.
#
XDG_DESKTOP_DIR="$HOME/desktop"
XDG_DOWNLOAD_DIR="$HOME/dl"
XDG_TEMPLATES_DIR="$HOME/templates"
XDG_PUBLICSHARE_DIR="$HOME/public"
XDG_DOCUMENTS_DIR="$HOME/docs"
XDG_MUSIC_DIR="$HOME/music"
XDG_PICTURES_DIR="$HOME/pics"
XDG_VIDEOS_DIR="$HOME/videos"

Building Git from scratch

2013-02-03T00:17:00-05:00

This is running on Ubuntu 12.04, using the most recent versions as of 2013-02-02.

Install git:

$ wget http://git-core.googlecode.com/files/git-1.8.1.2.tar.gz
$ tar xf git-1.8.1.2.tar.gz
$ cd git-1.8.1.2/
$ sudo apt-get install libcurl4-gnutls-dev libexpat1-dev gettext libz-dev
$ make prefix=/usr/local all
$ sudo make prefix=/usr/local install

Install the manpages:

$ wget http://git-core.googlecode.com/files/git-manpages-1.8.1.2.tar.gz
$ sudo tar xf git-manpages-1.8.1.2.tar.gz -C /usr/local/man

Using REMnux for Forensic Puzzle #6

2011-03-17T23:00:00-04:00

I thought it would be interesting to use Lenny Zeltser's excellent REMnux distribution to solve this puzzleposted by ForensicKB. I'll admit that I saw the solution before solving it, but since I don't have a copy of EnCase lying around, I wanted to use some free tools to accomplish the same thing.

Getting REMnux

Follow the instructions at the link above to get REMnux as a LiveCD or VMware-compatible virtual machine. Once you get it up and running (either just the console or the XFCE interface), we can get going...

Getting set up

Download the file into a new directory and unzip it.

remnux@remnux: ~$ mkdir Forensic Challenge6
remnux@remnux: ~$ cd ForensicChallenge6
remnux@remnux: ~/ForensicChallenge6$ wget http://www.lancemueller.com/blog/evidence/Suspicious_File.zip
remnux@remnux: ~/ForensicChallenge6$ unzip Suspicious_File.zip

Initial Steps

Just for fun, we can run "xorsearch" to see if we have an executable by looking for the string "This program cannot be run in DOS mode", a standard feature in Windows executables.

remnux@remnux: ~/ForensicChallenge6$ xorsearch Suspicious_File "This program"
Found XOR 6A position 0A4E: This program cannot be run in DOS mode....$

It's much later than we expected in the file, though (HINT: it's typically in the first 0x100 bytes.)

We'll use the "file" command along with the useful TrID to determine what type of we have.

remnux@remnux: ~/ForensicChallenge6$ file Suspicious_File
Suspicious_File: CDF V2 Document, corrupt: Cannot read summary info
remnux@remnux: ~/ForensicChallenge6$ trid Suspicious_File
TrID/32 - File Identifier v2.00/Linux - (C) 2003-06 By M.Pontello
Definitions found:  3887
Analyzing...

Collecting data from file: Suspicious_File
100.0% (.) Generic OLE2 / Multistream Compound File (8000/1)

Looks like an OLE2 Compound Binary File. I didn't want to write my own parser, so I started looking for a good command line one and found a good python scriptto do it for me.

remnux@remnux: ~/ForensicChallenge6$ wget http://www.decalage.info/files/OleFileIO_PL-0.21.zip
remnux@remnux: ~/ForensicChallenge6$ unzip OleFileIO_PL-0.21.zip
remnux@remnux: ~/ForensicChallenge6$ cd OleFileIO_PL-0.21/
remnux@remnux: ~/ForensicChallenge6/OleFileIO_PL-0.21$ python
Python 2.6.4 (r264:75706, Dec  7 2009, 18:45:15)
[GCC 4.4.1] on linux2
Type "help", "copyright", "credits" or "license" for more information.

A quick python interpreter session extracted the files from this compound file format.

>>> import OleFileIO_PL
>>> assert OleFileIO_PL.isOleFile('../Suspicious_File')
>>> ole = OleFileIO_PL.OleFileIO('../Suspicious_File')
>>> print ole.listdir()
[['Details'], ['File_0']]
>>> f = open('../Details','w')
>>> f.write(ole.openstream('Details').read())
>>> f.close()
>>> f = open('../File_0','w')
>>> f.write(ole.openstream('File_0').read())
>>> f.close()
>>> exit()

Now we have two files to analyze. We can use "xorsearch" again with the "-s" switch to perform the XOR on the executable file (File_0) and write the transformed file to disk.

remnux@remnux: ~/ForensicChallenge6/OleFileIO_PL-0.21$ cd ..
remnux@remnux: ~/ForensicChallenge6$ xorsearch -s File_0 "This program"Found XOR 6A position 004E: This program cannot be run in DOS mode....$

To convert the other file, we assume the same XOR key and use Perl to perform the conversion. I'm by no means a Perl guru, but some Googling helped a lot. It takes advantage of a lot of Perl's built-in default operators, to minimize the size of the commad.

remnux@remnux: ~/ForensicChallenge6$ cat Details | perl -e 'while (<STDIN>) { foreach (split //) {print chr(ord ^ 0x6a)}}' > Details.XOR.6A

Now we have the two files, and we can perform the required MD5 hash calculations, or any other analysis desired (i.e. on the executable).

remnux@remnux: ~/ForensicChallenge6$ md5sum File_0,XOR.6A
8dc601710e3e68b8d78b5cd73fb28616  File_0.XOR.6A
remnux@remnux:~/ForensicChallenge6$ md5sum Details.XOR.6A
f93a7bb8e02a8a23f87dad22b9ecd578  Details.XOR.6A

Summary

I certainly learned a lot about REMnux, and got to write a bit of code in the process. Hopefully you learned a thing or two reading this as well.

Double-buffered Panels in C#

2011-01-23T17:08:00-05:00

Having panels which update quickly without flickering requires double-buffering. To accomplish this in C#, you'll have to derive from the standard Panel class as shown below, and then replace the declaration and instantiation of the panel with your new class.

using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public class DoubleBufferedPanel : Panel
    {
        public DoubleBufferedPanel()
        {
            this.SetStyle(ControlStyles.AllPaintingInWmPaint |
                ControlStyles.OptimizedDoubleBuffer |
                ControlStyles.UserPaint, true);
        }
    }
}

and then replace System.Windows.Forms.Panel with DoubleBufferedPanel in the Designer.cs class.

Size of Frame around a default C# Windows Form

2011-01-23T16:36:00-05:00

So here's the scenario. I was looking to have the a panel with exact dimensions on a C# form (700x400). I wanted even and default spacing around the panel on the form. I figured out the default spacing was 12, so I set the size of the form to 724x424, only to find that something still looked wrong.

Turns out that the dimensions of the form include the border and title bar (seems obvious in retrospect, doesn't it). What I really wanted was to have the form's ClientSize equal to 724x424. To figure out what I needed the form dimensions to be in order to have a correctly-sized Client area to place my frame in, I used the following snippet:

MessageBox.Show(String.Format("{0}, {1}",
                              this.Width - this.ClientSize.Width,
                              this.Height - this.ClientSize.Height));

The final result:

The frame takes up 16 pixels horizontally (8 on each size) and 38 vertically (8 on the bottom and 30 on top), so the final size of the form I needed was 740x462.

Setting Outlook to Display Plain Text Email

2011-01-19T20:56:00-05:00

Although definitely not the only step to stopping malicious email, not displaying HTML or rich text in messages goes a long way. Here's the summary of where the settings are located:

Outlook 2003

Tools menu, Options, Preferences tab, E-mail area, E-mail Options, Message Handling area.

Outlook 2007

Tools menu, Trust Center, E-mail Security, Read as Plain Text.

Outlook 2010

File tab, Options, Trust Center, Trust Center Settings, E-mail Security, Read as Plain Text.

For more information, check out this Microsoft KB article.

Useful One-Line PHP files

2010-05-14T17:37:00-04:00

Here are a couple useful PHP commands that you can run on your server to get useful information.

This one gives basic information about the PHP installation, which can be used for troubleshooting or just verifying that PHP is running.

<?php phpinfo(); ?>

This one tells you the name of the web server user, which can be used to verify file permissions on particular files or directories.

<?php echo `whoami`; ?>

Hope this is useful!

PuTTY SSH Tunnel for MySQL

2010-05-09T14:42:00-04:00

I just stumbled across the MySQL GUI Tools Bundle which is very useful for managing a MySQL databases. In my opinion, it's much easier than using phpMyAdmin, which I had been doing previously. The only problem is that using it "requires" the machine the database is on (my web server) having an open external port (typically 3306) for the applications to have access to the database. "Requires" is in quotes because you can use PuTTY to open an SSH tunnel from your local machine to the database server, so that requests to port 3306 on your local machine are forwarded to the remote machine through the PuTTY connection.

Quick summary:

In PuTTY (before connecting to the server), go to Connections-> SSH-> Tunnels.
Add Source: "3306" (the local port you'll be using) and Destination: "127.0.0.1:3306" (the connection to be made from the other side of the tunnel.
Log into the server using PuTTY as you normally would. (Don't forget this step!)
Open MySQL Query Browser (or another of the tools), and for the connection info use Server: "localhost" and Port: "3306" (the local side of the tunnel), along with the appropriate username and password information.
The MySQL GUI tools should now work as normal. Enjoy.

For more information and screenshots, check out the link below.

[Source: realprogrammers.com]

Django Admin Media Files on Apache

2010-05-02T22:26:00-04:00

I had quite a bit of fun trying to get Apache to serve the admin files for my Django install. Here are the settings I used to finally get it to work. Note that the site is in a subdirectory of my domain. I'm not currently hosting any other media, so that will be another bridge to cross in the future.

In the Django settings.py file:

ADMIN_MEDIA_PREFIX = '/genweb/admin/media/'

In the Virtual Host file:

Alias /genweb/admin/media /usr/share/python-support/python-django/django/contrib/admin/media
<Location "/genweb/admin/media">
    SetHandler none
</Location>

PHP Equal-Sign Operators

2010-04-22T21:51:00-04:00

Reading some php code, you might get confused about the difference betweeen =, ==, and === (this single, double, and triple equal signs). Here's a quick summary.

= (Assignment) Just like in (pretty much) every other programming language.

== (Equality) Returns true if the two variables have the same value.

=== (Identity) Returns true if the two variables have the same value AND the same type (integer 0 is not equal to, in the === sense, float 0 or string 0).

Hope that clears up confusion. It did for me.

[Source: Wellho.net]

Cannot start Microsoft Office Outlook. Cannot open the Outlook window.

2010-04-09T10:11:00-04:00

I got this annoying error message this morning when trying to open Outlook 2007.

Cannot start Microsoft Office Outlook. Cannot open the Outlook window.

I tried logging out and back in, which didn't help. Neither did a restart. A quick Google search revealed the following solution:

Click Start, then Run (alternatively, press WINDOWS-R). On Windows 7, just click on the start button and use the quick search box.
Type "Outlook.exe /resetnavpane" and press Enter.

Voila. Outlook fixed.

[Source: Microsoft Answers]

Debuggers as Pesticides

2010-04-08T12:47:00-04:00

I thought this was funny:

Historical footnote: DDT was developed at MIT for the PDP-1 computer in 1961. At that time DDT stood for "DEC Debugging Tape". Since then, the idea of an on-line debugging program has propagated throughout the computer industry. DDT programs are now available for all DEC computers. Since media other than tape are now frequently used, the more descriptive name "Dynamic Debugging Technique" has been adopted, retaining the DDT abbreviation. Confusion between DDT-10 and another well known pesticide, dichloro-diphenyl-trichloroethane C14H9Cl5 should be minimal since each attacks a different, and apparently mutually exclusive, class of bugs.

[Source: The Jargon File]

Matlab Primes to File

2010-03-30T21:36:00-04:00

The MATLAB script below will export 10000 primes to a file named 'primes.txt':

x=primes(10000); % Insert your own value here
fopen('primes.txt','w+'); % Insert the file name heref
printf(ans, '%d\n',x); % Prints a new line between each prime (C-style formatting)
fclose all;

MySQL Change current auto-increment value

2010-02-20T13:30:00-05:00

You can use the following SQL query to set the next value to be used by an auto-incrementing field in MySQL. Useful if you make a mistake and want to delete a value you just added without leaving a gap in the sequence numbers, or if you want to start with an index higher than 1.

ALTER TABLE tablename AUTO_INCREMENT = value;

Firefox Updating Fix

2010-02-11T22:59:00-05:00

This is a problem I used to have with Firefox updates failing when I was running as a Limited User in Windows XP.

Here are the steps to fix the problem:

Close all running instances of Firefox.
Open an Administrator command prompt by right-clicking on a Command Prompt icon, choose Run As... and enter the credentials of a user with administrator rights.
Launch Process Monitor from the administrator command prompt by typing the full path to the executable (wherever you installed it). For example: c:\apps\procmon.exe (tab completion can be very helpful for this step).
Within Process Monitor, turn off "Show Registry Activity" and "Show File System Activity" from the toolbar. Only "Show Process and Thread Activity should be enabled". This step is not absolutely necessary, but it will eliminate a lot of extra noise.
Start Firefox, and click through the "Software Update Failed" dialog until the browser opens.
Switch back to Process Monitor and press CTRL-E or the click the toolbar button to stop capturing events. Close any Firefox windows that might be open.
Scroll through the list of processes and double-click on the first instance of "updater.exe" (it should have the value "Process Start" in the Operation column). Switch to the Process tab of the Event Properties window that opens.
Select the entire contents of the "Command Line:" textbox and copy it (CTRL-C or right-click, Copy). It should look something like this (all one line): "C:\Documents and Settings\Josh\Local Settings\Application Data\Mozilla\Firefox\Mozilla Firefox\updates\0\updater.exe" "C:\Documents and Settings\Josh\Local Settings\Application Data\Mozilla\Firefox\Mozilla Firefox\updates\0" "3824" "C:\Program Files\Mozilla Firefox" "C:\Program Files\Mozilla Firefox\firefox.exe"
Switch back to the administrator command prompt and right-click, Paste to paste the command-line. Press Enter.
You should see a dialog indicating that Firefox is updating. Close the browser that opens since it is still running as the administrator.
Now open Firefox normally. It should start up without the annoying error message.

Source: Flimflan.com

Adding a User to Sudoers in Fedora 11

2009-12-12T14:21:00-05:00

The following shows how to add a user to the "sudoers" file in Fedora 11 (and likely other versions of Fedora), allowing normal users to execute elevated commands with sudo ... instead of needing to switch to root (su -).

[greg@fedora ~]$ su -
[root@fedora ~]# chmod +w /etc/sudoers
[root@fedora ~]# echo 'greg ALL=(ALL) ALL' >> /etc/sudoers
[root@fedora ~]# chmod -w /etc/sudoers
[root@fedora ~]# exit

DOS/Windows Environment Variables

2009-12-03T16:07:00-05:00

To view all environment variables

set

To view a specific environment variable, use one of the following

set VARIABLE
echo %VARIABLE%

To set an environment variable

set VARIABLE=VAUE

Sine-Cosine-Exponential Identities

2009-11-04T20:21:00-05:00

Useful in my Digital Signal Processing class...

Source: Wikipedia - Euler's formula

Source: Wikipedia - Sinc function

How to Compress or Decompress .tar.gz (or .tgz) files

2009-10-17T13:47:00-04:00

To compress a folder of files into a single tar-zip file, use the command:

tar -czvf archive.tgz files/

To extract a tar-zip file into the current directory, use the command:

tar -xzvf archive.tgz

Using Google Image Search to Find Desktop Backgrounds

2009-09-01T10:59:00-04:00

I don't remember where I first saw this, but you can use the "imagesize" parameter in Google Image Search to find pictures that fit your desktop perfectly. In my case I have two size-by-side 19" monitors (not widescreen). Therefore my total screen space is 2560 x 1024. A Google image search for "beach sunset imagesize:2560x1024" gives me a wide variety of pictures to choose from without having to navigate desktop wallpaper sites.

[Google Image Search]

Determining Uptime for Windows

2009-08-14T16:32:00-04:00

After my computer restarted overnight I became curious as to what time it restarted (I had something running overnight and was upset that it didn't finish. A quick Google search revealed that there are several ways to reveal this information:

Uptime.exe Utility

Microsoft provides a small utility that determines uptime based on events in the Event Log. If the Event Log has been cleared then this method will not work. More information and the download link can be found here. You can copy it into the system directory (i.e. C:\WINDOWS) and run it from the command line anywhere or (if you don't have administrative privileges) save it in any directory and then run it using the command line from that directory.

SystemInfo command

Although uptime does not appear in the GUI System Information (Start->Programs->Accessories->System Tools->System Information), the command line tool "systeminfo" contains a line with the system uptime.

Batch Script

The following batch script will use the "systeminfo" command and find the uptime within the output of that command.

@echo
@systeminfo | @find "System Up Time:"
@echo
@pause

[Source : HardForum.com]

Network Connections

If you have a persistent network connection, typically it will start nearly as soon as the computer does. Therefore you can get a rough estimate using the information found in Start->Settings->Network Connections->(Connection Name) under the "Duration:" field.

(The above path is for Windows XP with the Classic Start Menu). Other versions of Windows have a slightly different path. Usually there is a "Network Connections" link on the left side of an Explorer Window. Otherwise there may be an icon representing your network connection in the system tray. Clicking on either of these should give an option to bring up the information for that connection.

TOP (Linux Program) CPU States

2009-08-12T07:36:00-04:00

The Unix/Linux program "top" is used to determine various information about processes your computer is executing. It is comparable to the "ps" command, but I prefer using top. It a good equivalent of the Task Manager on Windows, but much more powerful and customizable, if you're comfortable with the command line (though not as good as Process Explorer, in my opinion). I plan to write a more detailed comparison between ps and top in the future, but until then, here is the first question I had about top, as well as the solution I found on the web:

What do the "us/sy/ni", etc. abreviations mean in the (default) third line of top output (the one that begins with "Cpu(s):") ?

us- User CPU time. The time the CPU has spent running users’ processes with default priorities
sy- System CPU time. The time the CPU has spent running the kernel and its processes
ni- Nice CPU time. The time the CPU has spent running users’ proccess that have been prioritized up using nicecommand
wa- I/O wait. Amount of time the CPU has been waiting for I/O operations to complete
hi- Hardware IRQ. The amount of time the CPU has been servicing hardware interrupts
si- Software Interrupts. The amount of time the CPU has been servicing software interrupts
st- Steal Time. The amount of CPU ’stolen’ from this virtual machine by the hypervisor for other tasks (such as running another virtual machine) – a fairly recent addition to the top command, introduced with the increased virtualization focus in modern operating systems

[Source: UnixTutorial.org]