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• Measuring "real" phone signal strength on a mobile phone

  - by Serafeim

  I want to programmatically measure the phone signal strength in a mobile phone. I don't actually care about the mobile phone or the programming environment: It can be based on android or windows mobile or even J2ME and can be from any manufacturer (please no iPhone). However, it needs to be a real, commercial mobile phone and not a special measurement device. This problem is not as easy as it seems with a first look. I am aware that there already exist a number of methods that claim to return the phone signal strength. Some of these are: SystemState.PhoneSignalStrength for WM6 RIL_GetCellTowerInfo for WinCe (dwRxLevel member of returned RILCELLTOWERINFO struct) android.telephony.NeighboringCellInfo.getRssi() for android The problem with the above is that they only return a few (under 10) discrete values, meaning that, for instance, the return values of SystemState.PhoneSignalStrength can only be translated to (for instance) -100 dbm, -90 dbm, -80 dbm, -70 dbm and -60 dbm, something that is not useful for my application, since I'd like to have as much precision as possible. It doesn't matter if there is an undocumented solution that only works on only one phone, if you can tell me a way I'd be grateful. Thanks in advance

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• Android SeekBar Minimum and Continuous Float Value Attributes

  - by fordays

  I'm looking for a way to implement a minimum value in my SeekBar and also have the option to increment decimal numbers. For example, currently my SeekBar's minimum is set to 0, but I need it to start at the value 0.2. Also, I would like to have the functionality to be able to have the user select a number from 0.2 to 10.0 at a .1 precision so they can choose the numbers 5.6 or 7.1. Here are the style attributes for my SeekBar: <style name="SeekBar"> <item name="android:paddingLeft">30dp</item> <item name="android:paddingRight">30dp</item> <item name="android:layout_width">fill_parent</item> <item name="android:layout_height">wrap_content</item> <item name="android:layout_marginTop">0dp</item> <item name="android:layout_marginBottom">0dp</item> <item name="android:max">10</item> <item name="android:progress">1</item> </style>

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• Jenkins: Use it with SSL / https

  - by Tim

  I have a Fedora server running Jenkins which I install via yum. Everything is okay, I can access it with http://ci.mydomain.com. But now, I want to access it with https://ci.mydomain.com, so the login with username and password is encrypted. How can I do this? Best Regards Tim Update My /etc/sysconfig/jenkins file. Starting Jenkins works, but I can not access Jenkins with the webbrowser with https://ci.mydomain.com or http://ci.mydomain.com:443, ... ## Path: Development/Jenkins ## Description: Configuration for the Jenkins continuous build server ## Type: string ## Default: "/var/lib/jenkins" ## ServiceRestart: jenkins # # Directory where Jenkins store its configuration and working # files (checkouts, build reports, artifacts, ...). # JENKINS_HOME="/var/lib/jenkins" ## Type: string ## Default: "" ## ServiceRestart: jenkins # # Java executable to run Jenkins # When left empty, we'll try to find the suitable Java. # JENKINS_JAVA_CMD="" ## Type: string ## Default: "jenkins" ## ServiceRestart: jenkins # # Unix user account that runs the Jenkins daemon # Be careful when you change this, as you need to update # permissions of $JENKINS_HOME and /var/log/jenkins. # JENKINS_USER="jenkins" ## Type: string ## Default: "-Djava.awt.headless=true" ## ServiceRestart: jenkins # # Options to pass to java when running Jenkins. # JENKINS_JAVA_OPTIONS="-Djava.awt.headless=true" ## Type: integer(0:65535) ## Default: 8080 ## ServiceRestart: jenkins # # Port Jenkins is listening on. # JENKINS_PORT="8080" ## Type: integer(1:9) ## Default: 5 ## ServiceRestart: jenkins # # Debug level for logs -- the higher the value, the more verbose. # 5 is INFO. # JENKINS_DEBUG_LEVEL="5" ## Type: yesno ## Default: no ## ServiceRestart: jenkins # # Whether to enable access logging or not. # JENKINS_ENABLE_ACCESS_LOG="no" ## Type: integer ## Default: 100 ## ServiceRestart: jenkins # # Maximum number of HTTP worker threads. # JENKINS_HANDLER_MAX="100" ## Type: integer ## Default: 20 ## ServiceRestart: jenkins # # Maximum number of idle HTTP worker threads. # JENKINS_HANDLER_IDLE="20" ## Type: string ## Default: "" ## ServiceRestart: jenkins # # Pass arbitrary arguments to Jenkins. # Full option list: java -jar jenkins.war --help # JENKINS_ARGS="--httpsPort=443 --httpsKeyStore=/root/.keystore --httpsKeyStorePassword=MYPASSWORD"

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• SQLCLR and DateTime2

  - by Moe Sisko

  Using SQL Server 2008, Visual Studio 2005, .net 2.0 with SP2 (has support for new SQL Server 2008 data types). I'm trying to write an SQLCLR function that takes a DateTime2 as input and returns another DateTime2. e.g. : using System; using System.Data.SqlTypes; using Microsoft.SqlServer.Server; namespace MyCompany.SQLCLR { public class DateTimeHelpCLR { [SqlFunction(DataAccess = DataAccessKind.None)] public static SqlDateTime UTCToLocalDT(SqlDateTime val) { if (val.IsNull) return SqlDateTime.Null; TimeZone tz = System.TimeZone.CurrentTimeZone; DateTime res = tz.ToLocalTime(val.Value); return new SqlDateTime(res); } } } Now, the above compiles fine. I want these SqlDateTimes to map to SQL Server's DateTime2, so I try to run this T-SQL : CREATE function hubg.f_UTCToLocalDT ( @dt DATETIME2 ) returns DATETIME2 AS EXTERNAL NAME [SQLCLR].[MyCompany.SQLCLR.DateTimeHelpCLR].UTCToLocalDT GO This gives the following error : Msg 6551, Level 16, State 2, Procedure f_UTCToLocalDT, Line 1 CREATE FUNCTION for "f_UTCToLocalDT" failed because T-SQL and CLR types for return value do not match. Using DATETIME (instead of DATETIME2) works fine. But I'd rather use DATETIME2 to support the increased precision. What am I doing something wrong, or is DateTime2 not (fully) supported by SQLCLR ?

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• monitoring iphone 3g/wifi bandswitch

  - by user262325

  Hello everyone I hope add the function to monitor iphone used 3g/wifi band switch. I know I can do these in my app, but I wonder if there is way to monitor all band switch usage of iPhone? I noticed that there is an app http://itunes.apple.com/ca/app/download-meter-for-wi-fi-gprs/id327227530?mt=8 It claims: Works with any carrier (iPods are supported too!). Requires no login/password to your carrier's site. Does not require Internet connection to get traffic usage statistics (works even in Airplane mode) because it gets information on traffic from the device, not a carrier; this means it won't cost you anything to view current traffic consumed, even while roaming in a location where traffic is very expensive. Allows the user to adjust consumed traffic for today or the current month to match traffic amounts reported by your carrier. Stats on the screen are updated every second. Measures traffic in real time with up to byte precision. Separates traffic into incoming and outgoing, Wi-Fi traffic and mobile Internet traffic. It looks like it gets the band switch info from carrier site, but they also said it gets info from device. I am really confused. Welcome any comment. Thanks interdev

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• Conditional Regular Expression testing of a CSV

  - by Alastair Pitts

  I am doing some client side validation in ASP.NET MVC and I found myself trying to do conditional validation on a set of items (ie, if the checkbox is checked then validate and visa versa). This was problematic, to say the least. To get around this, I figured that I could "cheat" by having a hidden element that would contain all of the information for each set, thus the idea of a CSV string containing this information. I already use a custom [HiddenRequired] attribute to validate if the hidden input contains a value, with success, but I thought as I will need to validate each piece of data in the csv, that a regular expression would solve this. My regular expression work is extremely weak and after a good 2 hours I've almost given up. This is an example of the csv string: true,3,24,over,0.5 to explain: true denotes if I should validate the rest. I need to conditionally switch in the regex using this 3 and 24 are integers and will only ever fall in the range 0-24. over is a string and will either be over or under 0.5 is a decimal value, of unknown precision. In the validation, all values should be present and at least of the correct type Is there someone who can either provide such a regex or at least provide some hints, i'm really stuck!

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• DNAT to 127.0.0.1 with iptables / Destination access control for transparent SOCKS proxy

  - by cdauth

  I have a server running on my local network that acts as a router for the computers in my network. I want to achieve now that outgoing TCP requests to certain IP addresses are tunnelled through an SSH connection, without giving the people from my network the possibility to use that SSH tunnel to connect to arbitrary hosts. The approach I had in mind until now was to have an instance of redsocks listening on localhost and to redirect all outgoing requests to the IP addresses I want to divert to that redsocks instance. I added the following iptables rule: iptables -t nat -A PREROUTING -p tcp -d 1.2.3.4 -j DNAT --to-destination 127.0.0.1:12345 Apparently, the Linux kernel considers packets coming from a non-127.0.0.0/8 address to an 127.0.0.0/8 address as “Martian packets” and drops them. What worked, though, was to have redsocks listen on eth0 instead of lo and then have iptables DNAT the packets to the eth0 address instead (or using a REDIRECT rule). The problem about this is that then every computer on my network can use the redsocks instance to connect to every host on the internet, but I want to limit its usage to a certain set of IP addresses only. Is there any way to make iptables DNAT packets to 127.0.0.1? Otherwise, does anyone have an idea how I could achieve my goal without opening up the tunnel to everyone? Update: I have also tried to change the source of the packets, without any success: iptables -t nat -A POSTROUTING -p tcp -s 192.168.1.0/24 -d 1.2.3.4 -j SNAT --to-source 127.0.0.1 iptables -t nat -A POSTROUTING -p tcp -s 192.168.1.0/24 -d 127.0.0.1 -j SNAT --to-source 127.0.0.1

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• How can I map a Windows group login to the dbo schema in a database?

  - by Christian Hayter

  I have a database for which I want to restrict access to 3 named individuals. I thought I could do the following: Create a local Windows group on the database server and add the named individuals to it. Create a Windows login in SQL Server mapped to the local Windows group. Map the login to the "dbo" schema in the database, so that the users can access all objects without having to qualify them with the schema name. When I try to do step 3, I get the following error: Msg 15353, Level 16, State 1, Line 1 An entity of type database cannot be owned by a role, a group, an approle, or by principals mapped to certificates or asymmetric keys. I have tried to do this via the IDE, the sp_changedbowner sproc, and the ALTER AUTHORIZATION command, and I get the same error each time. After searching MSDN and Google, I find that this restriction is by design. Great, that's useful. Can anyone tell me: Why this restriction exists? It seems very arbitrary. More importantly, can I accomplish my requirement some other way? Other info that might be pertinent: The server is fully up to date with service packs and hotfixes. All objects in the database are owned by the "dbo" schema, and it's not feasible to change that. The database is running in compatibility level 80, and it's not feasible to change that to 90 yet. I am free to make any other changes (within reason, depending on what they are).

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• What's up with stat on MacOSX/Darwin? Or filesystems without names...

  - by Charles Stewart

  In response to a question I asked on SO, Give the mount point of a path, one respondant suggested using stat to get the device name associated with the volume of a given path. This works nicely on Linux, but gives crazy results on MacOSX 10.4. For my system, df and mount give: cas cas$ df Filesystem 512-blocks Used Avail Capacity Mounted on /dev/disk0s3 58342896 49924456 7906440 86% / devfs 194 194 0 100% /dev fdesc 2 2 0 100% /dev <volfs> 1024 1024 0 100% /.vol automount -nsl [166] 0 0 0 100% /Network automount -fstab [170] 0 0 0 100% /automount/Servers automount -static [170] 0 0 0 100% /automount/static /dev/disk2s1 163577856 23225520 140352336 14% /Volumes/Snapshot /dev/disk2s2 409404102 5745938 383187960 1% /Volumes/Sparse cas cas$ mount /dev/disk0s3 on / (local, journaled) devfs on /dev (local) fdesc on /dev (union) <volfs> on /.vol automount -nsl [166] on /Network (automounted) automount -fstab [170] on /automount/Servers (automounted) automount -static [170] on /automount/static (automounted) /dev/disk2s1 on /Volumes/Snapshot (local, nodev, nosuid, journaled) /dev/disk2s2 on /Volumes/Sparse (asynchronous, local, nodev, nosuid) Trying to get the devices from the mount points, though: cas cas$ df | grep -e/ | awk '{print $NF}' | while read line; do echo $line $(stat -f"%Sdr" $line); done / disk0s3r /dev ???r /dev ???r /.vol ???r /Network ???r /automount/Servers ???r /automount/static ???r /Volumes/Snapshot disk2s1r /Volumes/Sparse disk2s2r Here, I'm feeding each of the mount points scraped from df to stat, outputting the results of the "%Sdr" format string, which is supposed to be the device name: Cf. stat(1) man page: The special output specifier S may be used to indicate that the output, if applicable, should be in string format. May be used in combination with: ... dr Display actual device name. What's going on? Is it a bug in stat, or some Darwin VFS weirdness? Postscript Per Andrew McGregor, try passing "%Sd" to stat for more weirdness. It lists some apparently arbitrary subset of files from CWD...

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• Is there a simple LDAP-to-HTTP gateway out there?

  - by larsks

  We have a local LDAP directory that provides basic contact information about our user community. We would like to integrate this into some third-party hosted services that allow us to implement widgets that run arbitrary Javascript. In order to connect Javascript to our LDAP directory, I would like to set up a simple LDAP-to-HTTP proxy that would accept HTTP GET requests, translate them into an appropriate LDAP query, and respond with directory information as JSON-encoded data. In an ideal world, something like this: GET /[email protected] Would get me something like this: { "cn": "Bob Person", "title": "System Administrator", "sn": "Person", "mail": "[email protected]", "telepehoneNumber": "617-555-1212", "givenName": "Bob" } (And this obviously assumes that the web application has locally configured information about what base DN to use, how to authenticate, etc). I guess I could write one...but surely something like this already exists? UPDATE The consensus seems to be that there isn't a pre-existing solution out there and that I should just get off my lazy derriere and write one. So I did, and it's here. It's not especially pretty, but it works for my prototyping and I figure maybe someone else will find it useful someday.

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• Saturated addition of two signed Java 'long' values

  - by finnw

  How can one add two long values (call them x and y) in Java so that if the result overflows then it is clamped to the range Long.MIN_VALUE..Long.MAX_VALUE? For adding ints one can perform the arithmetic in long precision and cast the result back to an int, e.g.: int saturatedAdd(int x, int y) { long sum = (long) x + (long) y; long clampedSum = Math.max((long) Integer.MIN_VALUE, Math.min(sum, (long) Integer.MAX_VALUE)); return (int) clampedSum; } or import com.google.common.primitives.Ints; int saturatedAdd(int x, int y) { long sum = (long) x + (long) y; return Ints.saturatedCast(sum); } but in the case of long there is no larger primitive type that can hold the intermediate (unclamped) sum. Since this is Java, I cannot use inline assembly (in particular SSE's saturated add instructions.) It can be implemented using BigInteger, e.g. static final BigInteger bigMin = BigInteger.valueOf(Long.MIN_VALUE); static final BigInteger bigMax = BigInteger.valueOf(Long.MAX_VALUE); long saturatedAdd(long x, long y) { BigInteger sum = BigInteger.valueOf(x).add(BigInteger.valueOf(y)); return bigMin.max(sum).min(bigMax).longValue(); } however performance is important so this method is not ideal (though useful for testing.) I don't know whether avoiding branching can significantly affect performance in Java. I assume it can, but I would like to benchmark methods both with and without branching. Related: http://stackoverflow.com/questions/121240/saturating-addition-in-c

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• Window Management for Mac OS X

  - by Paolo Maffei

  Ok, I feel dumb. I've put many hours into this and found nothing, yet. When I was using Windows I had this little tool called WinSplit Revolution. What it did was letting you divide your screen into how many and of how much size you choose "virtual monitors". You set one time of you want to divide your monitor, then everytime WinSplit is opened the monitor is automatically divided into Virtual Monitors. Screenshots: http://www.google.com/images?hl=en&q=winsplit%20revolution&um=1&ie=UTF-8&source=og&sa=N&tab=wi&biw=1045&bih=499 I'm now using a 30' which i want almost always divided into 4 equal size "virtual monitors" (plus my mbp 13' those will be 5 1280x800 virtual monitors) Now I've switched to Mac OS X and can't find anything that does just this efficiently. I tried Divvy but I found no way to divide my screen into arbitrary "virtual monitors", I need a couple of clicks to select a 3x3 space on a 9x9 grid. Before starting coding something like this can you tell me if you already know of some software that does window management like this?

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• Will fixed-point arithmetic be worth my trouble?

  - by Thomas

  I'm working on a fluid dynamics Navier-Stokes solver that should run in real time. Hence, performance is important. Right now, I'm looking at a number of tight loops that each account for a significant fraction of the execution time: there is no single bottleneck. Most of these loops do some floating-point arithmetic, but there's a lot of branching in between. The floating-point operations are mostly limited to additions, subtractions, multiplications, divisions and comparisons. All this is done using 32-bit floats. My target platform is x86 with at least SSE1 instructions. (I've verified in the assembler output that the compiler indeed generates SSE instructions.) Most of the floating-point values that I'm working with have a reasonably small upper bound, and precision for near-zero values isn't very important. So the thought occurred to me: maybe switching to fixed-point arithmetic could speed things up? I know the only way to be really sure is to measure it, that might take days, so I'd like to know the odds of success beforehand. Fixed-point was all the rage back in the days of Doom, but I'm not sure where it stands anno 2010. Considering how much silicon is nowadays pumped into floating-point performance, is there a chance that fixed-point arithmetic will still give me a significant speed boost? Does anyone have any real-world experience that may apply to my situation?

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• Understanding floating point problems

  - by Maxim Gershkovich

  Could someone here please help me understand how to determine when floating point limitations will cause errors in your calculations. For example the following code. CalculateTotalTax = function (TaxRate, TaxFreePrice) { return ((parseFloat(TaxFreePrice) / 100) * parseFloat(TaxRate)).toFixed(4); }; I have been unable to input any two values that have caused for me an incorrect result for this method. If I remove the toFixed(4) I can infact see where the calculations start to lose accuracy (somewhere around the 6th decimal place). Having said that though, my understanding of floats is that even small numbers can sometimes fail to be represented or have I misunderstood and can 4 decimal places (for example) always be represented accurately. MSDN explains floats as such... This means they cannot hold an exact representation of any quantity that is not a binary fraction (of the form k / (2 ^ n) where k and n are integers) Now I assume this applies to all floats (inlcuding those used in javascript). Fundamentally my question boils down to this. How can one determine if any specific method will be vulnerable to errors in floating point operations, at what precision will those errors materialize and what inputs will be required to produce those errors? Hopefully what I am asking makes sense.

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• How to transfer Windows Vista disk image to new machine

  - by Mike Hobbs

  I'm trying to upgrade a user's machine to some better hardware. I know of Easy Transfer, but I'd rather not have to reinstall all the programs that are already present. (Some of which are no longer available, anyway). Instead, I'm trying to transfer the entire disk image from one machine to the other, but I ran into issues. If I copy the partition image over to the new machine using Clonezilla, I get errors on boot saying that I need to insert the Vista install disk and run repair. I do that, but it then says that it is unable to repair whatever it is that's broken. Next, I tried to sysprep the old machine before creating the image, but sysprep fails saying that it encountered some sort of system error. Should it be possible to sysprep any arbitrary machine, or does it only work on a relatively clean install? Could it be a missing driver that is tripping me up? The new machine is a fairly stock desktop that shouldn't need any special drivers beyond what's already present in standard Vista. Are there any foolproof methods for doing this sort of thing?

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• If I scp a file through an intermediate server, is the file stored temporarily on the server?

  - by Blacklight Shining

  For the sake of simplicity (I find it easier to remember names than arbitrary letters), I will dispense with letters and use names to refer to the machines in this scenario. Say I have two machines, applejack and pinkie-pie, each on their own separate LANs and not in the same physical location. I also have a server, cadance, with a direct Internet-facing connection. I want to copy a file from applejack to pinkie-pie, so to avoid dealing with port forwarding and such, I set up an ssh tunnel from pinkie-pie to cadance (ssh -R etc cadance). Now I can connect to pinkie-pie from anywhere, by connecting to cadance and specifying an alternate port to use. I can also easily copy files to pinkie-pie with scp -P $that_port $some_file cadance:$some_path. My understanding of how it works is this: A secure connection is made from applejack to cadance I am authenticated to cadance A secure connection is made from applejack to pinkie-pie that spans the existing reverse tunnel and the new connection from step 1. I am authenticated to pinkie-pie Files are copied directly from applejack to pinkie-pie over this connection. Am I correct here? How secure is this approach? If I'm wrong…are files copied this way decrypted at cadance before being passed on to pinkie-pie? Is there a possibility that traces of unencrypted data could remain on cadance?

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• how to handle an asymptote/discontinuity with Matplotlib

  - by Geddes

  Hello all. Firstly - thanks again for all your help. Sorry not to have accepted the responses to my previous questions as I did not know how the system worked (thanks to Mark for pointing that out!). I have since been back and gratefully acknowledged the kind help I have received. My question: when plotting a graph with a discontinuity/asymptote/singularity/whatever, is there any automatic way to prevent Matplotlib from 'joining the dots' across the 'break'? (please see code/image below). I read that Sage has a [detect_poles] facility that looked good, but I really want it to work with Matplotlib. Thanks and best wishes, Geddes import matplotlib.pyplot as plt import numpy as np from sympy import sympify, lambdify from sympy.abc import x fig = plt.figure(1) ax = fig.add_subplot(111) # set up axis ax.spines['left'].set_position('zero') ax.spines['right'].set_color('none') ax.spines['bottom'].set_position('zero') ax.spines['top'].set_color('none') ax.xaxis.set_ticks_position('bottom') ax.yaxis.set_ticks_position('left') # setup x and y ranges and precision xx = np.arange(-0.5,5.5,0.01) # draw my curve myfunction=sympify(1/(x-2)) mylambdifiedfunction=lambdify(x,myfunction,'numpy') ax.plot(xx, mylambdifiedfunction(xx),zorder=100,linewidth=3,color='red') #set bounds ax.set_xbound(-1,6) ax.set_ybound(-4,4) plt.show()

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• How can I process an image in .NET for a full-page print with a quality like Windows Photo Gallery d

  - by Triynko

  I'm writing a printing routing in C#, using the .NET PrintDocument class, handling the OnPrintPage event. I've managed to maximize the margins and print the Image in landscape mode, but it simply does not look as good as when I print the same image file from Windows Photo Gallery (formerly Windows Picture and Fax Viewer), the default image preview program in Windows Vista. I noticed an option there for selecting "Sharpen Image for Printing", but what does that do? I've thought about printing copies of the image from Windows Photo Gallery first, then sending the sheets through the printer a second time to print the custom overlays I need, but it's hard to make it line up every time, since the printer sucks the sheet in without the kind of precision I need... so I really need to do ALL the drawing commands within C#, including the image. Does anyone know how to perform pre-processing on the bitmap so that it prints as nicely as Windows Photo Gallery does it? Are there any simple print drivers that can intercept Photo Gallery printing output as a standard image file (bmp, png, etc.) that can be read by the .NET Image class? I'm all for creativity here.

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• What's up with stat on Macos/Darwin? Or filesystems without names...

  - by Charles Stewart

  In response to a question I asked on SO, Give the mount point of a path, one respondant suggested using stat to get the device name associated with the volume of a given path. This works nicely on Linux, but gives crazy results on Macos 10.4. For my system, df and mount give: cas cas$ df Filesystem 512-blocks Used Avail Capacity Mounted on /dev/disk0s3 58342896 49924456 7906440 86% / devfs 194 194 0 100% /dev fdesc 2 2 0 100% /dev 1024 1024 0 100% /.vol automount -nsl [166] 0 0 0 100% /Network automount -fstab [170] 0 0 0 100% /automount/Servers automount -static [170] 0 0 0 100% /automount/static /dev/disk2s1 163577856 23225520 140352336 14% /Volumes/Snapshot /dev/disk2s2 409404102 5745938 383187960 1% /Volumes/Sparse cas cas$ mount /dev/disk0s3 on / (local, journaled) devfs on /dev (local) fdesc on /dev (union) on /.vol automount -nsl [166] on /Network (automounted) automount -fstab [170] on /automount/Servers (automounted) automount -static [170] on /automount/static (automounted) /dev/disk2s1 on /Volumes/Snapshot (local, nodev, nosuid, journaled) /dev/disk2s2 on /Volumes/Sparse (asynchronous, local, nodev, nosuid) Trying to get the devices from the mount points, though: cas cas$ df | grep -e/ | awk '{print $NF}' | while read line; do echo $line $(stat -f"%Sdr" $line); done / disk0s3r /dev ???r /dev ???r /.vol ???r /Network ???r /automount/Servers ???r /automount/static ???r /Volumes/Snapshot disk2s1r /Volumes/Sparse disk2s2r Here, I'm feeding each of the mount points scraped from df to stat, outputing the results of the "%Sdr" format string, which is supposed to be the device name: Cf. stat(1) man page: The special output specifier S may be used to indicate that the output, if applicable, should be in string format. May be used in combination with: ... dr Display actual device name. What's going on? Is it a bug in stat, or some Darwin VFS weirdness? Postscript Per Andrew McGregor, try passing "%Sd" to stat for more weirdness. It lists some apparently arbitrary subset of files from CWD...

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• What's up with stat on Mac OS X/Darwin? Or filesystems without names...

  - by Charles Stewart

  In response to a question I asked on SO, Give the mount point of a path, one respondant suggested using stat to get the device name associated with the volume of a given path. This works nicely on Linux, but gives crazy results on Mac OS X 10.4. For my system, df and mount give: cas cas$ df Filesystem 512-blocks Used Avail Capacity Mounted on /dev/disk0s3 58342896 49924456 7906440 86% / devfs 194 194 0 100% /dev fdesc 2 2 0 100% /dev <volfs> 1024 1024 0 100% /.vol automount -nsl [166] 0 0 0 100% /Network automount -fstab [170] 0 0 0 100% /automount/Servers automount -static [170] 0 0 0 100% /automount/static /dev/disk2s1 163577856 23225520 140352336 14% /Volumes/Snapshot /dev/disk2s2 409404102 5745938 383187960 1% /Volumes/Sparse cas cas$ mount /dev/disk0s3 on / (local, journaled) devfs on /dev (local) fdesc on /dev (union) <volfs> on /.vol automount -nsl [166] on /Network (automounted) automount -fstab [170] on /automount/Servers (automounted) automount -static [170] on /automount/static (automounted) /dev/disk2s1 on /Volumes/Snapshot (local, nodev, nosuid, journaled) /dev/disk2s2 on /Volumes/Sparse (asynchronous, local, nodev, nosuid) Trying to get the devices from the mount points, though: cas cas$ df | grep -e/ | awk '{print $NF}' | while read line; do echo $line $(stat -f"%Sdr" $line); done / disk0s3r /dev ???r /dev ???r /.vol ???r /Network ???r /automount/Servers ???r /automount/static ???r /Volumes/Snapshot disk2s1r /Volumes/Sparse disk2s2r Here, I'm feeding each of the mount points scraped from df to stat, outputting the results of the "%Sdr" format string, which is supposed to be the device name: Cf. stat(1) man page: The special output specifier S may be used to indicate that the output, if applicable, should be in string format. May be used in combination with: ... dr Display actual device name. What's going on? Is it a bug in stat, or some Darwin VFS weirdness? Postscript Per Andrew McGregor, try passing "%Sd" to stat for more weirdness. It lists some apparently arbitrary subset of files from CWD...

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• Password Cracking Windows Accounts

  - by Kevin

  At work we have laptops with encrypted harddrives. Most developers here (on occasion I have been guilty of it too) leave their laptops in hibernate mode when they take them home at night. Obviously, Windows (i.e. there is a program running in the background which does it for windows) must have a method to unencrypt the data on the drive, or it wouldn't be able to access it. That being said, I always thought that leaving a windows machine on in hibernate mode in a non-secure place (not at work on a lock) is a security threat, because someone could take the machine, leave it running, hack the windows accounts and use it to encrypt the data and steal the information. When I got to thinking about how I would go about breaking into the windows system without restarting it, I couldn't figure out if it was possible. I know it is possible to write a program to crack windows passwords once you have access to the appropriate file(s). But is it possible to execute a program from a locked Windows system that would do this? I don't know of a way to do it, but I am not a Windows expert. If so, is there a way to prevent it? I don't want to expose security vulnerabilities about how to do it, so I would ask that someone wouldn't post the necessary steps in details, but if someone could say something like "Yes, it's possible the USB drive allows arbitrary execution," that would be great! EDIT: The idea being with the encryption is that you can't reboot the system, because once you do, the disk encryption on the system requires a login before being able to start windows. With the machine being in hibernate, the system owner has already bypassed the encryption for the attacker, leaving windows as the only line of defense to protect the data.

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• tcp connect hangs on SYN_SENT if something listens, gets CONN_REFUSED if nothing listens

  - by Amos Shapira

  I'm hitting a very strange problem - when I try to connect to one of our servers the client hangs with SYN_SENT if something listens on the port (e.g. Apache on port 80, sshd on port 22 or SMTP on port 25) but if I try to connect to a port on which nothing listens then I immediately get a "CONNECTION refused" error. Connecting to other applications (e.g. rsyncd on some arbitrary port) succeeds. I ran tcpdump on the server and see that the SYN packets arrive to it but it only sends a response if nothing listens on that port. e.g.: on the server I run: # tcpdump -nn port 81 06:49:34.641080 IP 10.x.y.z.49829 server.81: S 3966400723:3966400723(0) win 12320 06:49:34.641118 IP server.81 x.y.z.49829: R 0:0(0) ack 3966400724 win 0 But if I listen on this port, e.g. with nc -4lvvv 81 & Then the output of tcpdump is: 06:44:31.063614 IP x.y.z.45954 server.81: S 3493682313:3493682313(0) win 12320 (and repeats until I stop it) The server is CentOS 5, the client is Ubuntu 11.04, the connection is done between two LAN's over per-user TCP OpenVPN. Connection to other servers on that network do not have a problem. Connecting from the other servers on the same network to that server works fine. Connections from other clients in our office over openvpn is also not a problem. What am I missing? Thanks.

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• Monitoring / metric collection for system collectives that change a lot in time (a.k.a. cloud)

  - by Florin Andrei

  When your server fleet doesn't change a lot in time, like when you're using bare-metal hosting, classic monitoring and metric collection solutions (Nagios, Munin) work well. But if the number of systems varies a lot in time, and may in fact vary rapidly, classic software is more difficult to setup and use. E.g., trying to make Nagios (monitoring) keep up with a rapidly evolving cloud infrastructure can be cumbersome. Same for Munin (metric collection). It's not just the configuration, but the way the information is conveyed to the user, or displayed, is inadequate for the cloud. What are some possible alternatives that work well with the cloud? The goals are to collect and display metrics (analog to Munin), and generate alerts when certain metrics go out of bounds or when certain services are unavailable (analog to Nagios), and do everything in a cloud-friendly manner. Some cloud providers offer monitoring / metric collection as services, but not always, and if you use more than one provider you don't want to become too dependent of just one vendor. So provider-independent solutions are required. EDIT: I am asking this question in a general fashion - not limited to any given cloud infrastructure (like OpenStack), but in the general case of using arbitrary cloud providers.

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• Is this a File Header / Magic Number?

  - by Hammer Bro.

  I've got 120,000 files (way more, actually; this is just an arbitrary subset) of an unknown type. Linux file does not identify them (not that they're necessarily Linux files), nor do any other methods I've tried. There are only two hints about them that I currently have. One is that I suspect some compression is employed -- I have metadata that claims the file sizes are always some amount larger than what I observe. The other is that in 100,000 of these files, the first 16 bytes are always: ff ee ee dd 00 00 00 00 01 00 00 00 00 00 00 00 That really looks like a file header/magic number to me, but I just can't place it. Does anyone know what kind of files this would indicate? Alternatively, can anyone convince me that these suspiciously common bytes certainly do not indicate a specific file type? UPDATE I don't know the exact reverse-engineering details, but most of the files in our case are zips after the first 29(? or so) bytes are ignored. So in practice the problem is solved (we know how to process the files) but in theory the question is still unanswered -- I don't know which application routinely prepends about 29 bytes to its zips. [I'm not sure if I should leave the question open or not at this point.]

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• Debugging "clogged" TCP connections

  - by Nikratio

  I'm having trouble with an internet connection that seems to randomly "freeze" arbitrary tcp connections. The connections stay established, but no data is coming through. When this happens, netstat still shows the connection status as ESTABLISHED on both the local computer: Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name Timer tcp 0 53 192.168.0.10:41129 173.255.235.238:143 ESTABLISHED 8219/gnutls-cli on (79.31/13/0) ..and the remote server: Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name Timer tcp 0 0 173.255.235.238:143 68.5.174.98:41129 ESTABLISHED 5303/imapd off (0.00/0/0) However, it seems that no data at all is transferred. If I run strace on the local and remote process, both just show a repeating sequence of select calls (with different fds of course), e.g. select(6, [0 5], NULL, NULL, {0, 50000}) = 0 (Timeout) select(6, [0 5], NULL, NULL, {0, 50000}) = 0 (Timeout) select(6, [0 5], NULL, NULL, {0, 50000}) = 0 (Timeout) The internet connection overall does not seem affected, I can still establish new connections to the same service on the same server without any problems. However, the affected local applications seem to be unaware of the problem and just hang. When I look at a packet capture of this connection on the client side, the last thing that happens is that the client transmits some data, then nothing happens for about 1100 seconds, and then several TCP Retransmission requests go out, with intervals increasing from 4 seconds to 130 seconds. No activity is captured after that. After about 10 minutes, the connection on the remote end disappears from the netstat (I wasn't able to catch any intermediate state), but still stays ESTABLISHED on the local end. Finally, after some more minutes, the local application aborts with a timeout and disappears from the local netstat output as well. Does anyone have a suggestion of how I could debug this further to find out where the problem lies and how to fix it? Additionaly and/or as a temporary workaround: is is there some way to globally reduce the timeout on client and/or server to reduce the time before the local application aborts?

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