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• PostSharp, Obfuscation, and IL

  - by Simon Cooper

  Aspect-oriented programming (AOP) is a relatively new programming paradigm. Originating at Xerox PARC in 1994, the paradigm was first made available for general-purpose development as an extension to Java in 2001. From there, it has quickly been adapted for use in all the common languages used today. In the .NET world, one of the primary AOP toolkits is PostSharp. Attributes and AOP Normally, attributes in .NET are entirely a metadata construct. Apart from a few special attributes in the .NET framework, they have no effect whatsoever on how a class or method executes within the CLR. Only by using reflection at runtime can you access any attributes declared on a type or type member. PostSharp changes this. By declaring a custom attribute that derives from PostSharp.Aspects.Aspect, applying it to types and type members, and running the resulting assembly through the PostSharp postprocessor, you can essentially declare 'clever' attributes that change the behaviour of whatever the aspect has been applied to at runtime. A simple example of this is logging. By declaring a TraceAttribute that derives from OnMethodBoundaryAspect, you can automatically log when a method has been executed: public class TraceAttribute : PostSharp.Aspects.OnMethodBoundaryAspect { public override void OnEntry(MethodExecutionArgs args) { MethodBase method = args.Method; System.Diagnostics.Trace.WriteLine( String.Format( "Entering {0}.{1}.", method.DeclaringType.FullName, method.Name)); } public override void OnExit(MethodExecutionArgs args) { MethodBase method = args.Method; System.Diagnostics.Trace.WriteLine( String.Format( "Leaving {0}.{1}.", method.DeclaringType.FullName, method.Name)); } } [Trace] public void MethodToLog() { ... } Now, whenever MethodToLog is executed, the aspect will automatically log entry and exit, without having to add the logging code to MethodToLog itself. PostSharp Performance Now this does introduce a performance overhead - as you can see, the aspect allows access to the MethodBase of the method the aspect has been applied to. If you were limited to C#, you would be forced to retrieve each MethodBase instance using Type.GetMethod(), matching on the method name and signature. This is slow. Fortunately, PostSharp is not limited to C#. It can use any instruction available in IL. And in IL, you can do some very neat things. Ldtoken C# allows you to get the Type object corresponding to a specific type name using the typeof operator: Type t = typeof(Random); The C# compiler compiles this operator to the following IL: ldtoken [mscorlib]System.Random call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle( valuetype [mscorlib]System.RuntimeTypeHandle) The ldtoken instruction obtains a special handle to a type called a RuntimeTypeHandle, and from that, the Type object can be obtained using GetTypeFromHandle. These are both relatively fast operations - no string lookup is required, only direct assembly and CLR constructs are used. However, a little-known feature is that ldtoken is not just limited to types; it can also get information on methods and fields, encapsulated in a RuntimeMethodHandle or RuntimeFieldHandle: // get a MethodBase for String.EndsWith(string) ldtoken method instance bool [mscorlib]System.String::EndsWith(string) call class [mscorlib]System.Reflection.MethodBase [mscorlib]System.Reflection.MethodBase::GetMethodFromHandle( valuetype [mscorlib]System.RuntimeMethodHandle) // get a FieldInfo for the String.Empty field ldtoken field string [mscorlib]System.String::Empty call class [mscorlib]System.Reflection.FieldInfo [mscorlib]System.Reflection.FieldInfo::GetFieldFromHandle( valuetype [mscorlib]System.RuntimeFieldHandle) These usages of ldtoken aren't usable from C# or VB, and aren't likely to be added anytime soon (Eric Lippert's done a blog post on the possibility of adding infoof, methodof or fieldof operators to C#). However, PostSharp deals directly with IL, and so can use ldtoken to get MethodBase objects quickly and cheaply, without having to resort to string lookups. The kicker However, there are problems. Because ldtoken for methods or fields isn't accessible from C# or VB, it hasn't been as well-tested as ldtoken for types. This has resulted in various obscure bugs in most versions of the CLR when dealing with ldtoken and methods, and specifically, generic methods and methods of generic types. This means that PostSharp was behaving incorrectly, or just plain crashing, when aspects were applied to methods that were generic in some way. So, PostSharp has to work around this. Without using the metadata tokens directly, the only way to get the MethodBase of generic methods is to use reflection: Type.GetMethod(), passing in the method name as a string along with information on the signature. Now, this works fine. It's slower than using ldtoken directly, but it works, and this only has to be done for generic methods. Unfortunately, this poses problems when the assembly is obfuscated. PostSharp and Obfuscation When using ldtoken, obfuscators don't affect how PostSharp operates. Because the ldtoken instruction directly references the type, method or field within the assembly, it is unaffected if the name of the object is changed by an obfuscator. However, the indirect loading used for generic methods was breaking, because that uses the name of the method when the assembly is put through the PostSharp postprocessor to lookup the MethodBase at runtime. If the name then changes, PostSharp can't find it anymore, and the assembly breaks. So, PostSharp needs to know about any changes an obfuscator does to an assembly. The way PostSharp does this is by adding another layer of indirection. When PostSharp obfuscation support is enabled, it includes an extra 'name table' resource in the assembly, consisting of a series of method & type names. When PostSharp needs to lookup a method using reflection, instead of encoding the method name directly, it looks up the method name at a fixed offset inside that name table: MethodBase genericMethod = typeof(ContainingClass).GetMethod(GetNameAtIndex(22)); PostSharp.NameTable resource: ... 20: get_Prop1 21: set_Prop1 22: DoFoo 23: GetWibble When the assembly is later processed by an obfuscator, the obfuscator can replace all the method and type names within the name table with their new name. That way, the reflection lookups performed by PostSharp will now use the new names, and everything will work as expected: MethodBase genericMethod = typeof(#kGy).GetMethod(GetNameAtIndex(22)); PostSharp.NameTable resource: ... 20: #kkA 21: #zAb 22: #EF5a 23: #2tg As you can see, this requires direct support by an obfuscator in order to perform these rewrites. Dotfuscator supports it, and now, starting with SmartAssembly 6.6.4, SmartAssembly does too. So, a relatively simple solution to a tricky problem, with some CLR bugs thrown in for good measure. You don't see those every day!

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• Sorting a Linked List [closed]

  - by Mohit Sehgal

  I want to sort a linked list. Here Node is class representing a node in a Linked List I have written a code to bubble sort a linked list. Program does not finishes execution. Kindly point out the mistakes. class Node { public: int data; public: Node *next; Node() { data=0;next=0; } Node(int d) { data=d; } void setData(int d) { data=d; } void print() { cout<<data<<endl; } bool operator==(Node n) { return this->data==n.data; } bool operator >(Node d) { if((this->data) > (d.data)) return true; return false; } }; class LList { public: int noOfNodes; Node *start;/*Header Node*/ LList() { start=new Node; noOfNodes=0;start=0; } void addAtFront(Node* n) { n->next=(start); start=n; noOfNodes++; } void addAtLast(Node* n) { Node *cur=(start); n->next=NULL; if(start==NULL) { start=n; noOfNodes++; return; } while(cur->next!=NULL) { cur=cur->next; } cur->next=n; noOfNodes++; } void addAtPos(Node *n,int pos) { if(pos==1) { addAtFront(n);return; } Node *cur=(start); Node *prev=NULL; int curPos=0; n->next=NULL; while(cur!=NULL) { curPos++; if(pos==curPos+1) { prev=cur; } if(pos==curPos) { n->next=cur; prev->next=n; break; } cur=cur->next; } noOfNodes++; } void removeFirst() { Node *del=start; start=start->next; delete del; noOfNodes--; return; } void removeLast() { Node *cur=start,*prev=NULL; while(cur->next!=NULL) { prev=cur; cur=cur->next; } prev->next=NULL; Node *del=cur->next; delete del; noOfNodes--; return; } void removeNodeAt(int pos) { if(pos<1) return; if(pos==1) { removeFirst();return;} int curPos=1; Node* cur=start->next; Node* prev=start; Node* del=NULL; while(curPos<pos&&cur!=NULL) { curPos++; if(curPos==pos) { del=cur; prev->next=cur->next; cur->next=NULL; delete del; noOfNodes--; break; } prev=prev->next; cur=cur->next; } } void removeNode(Node *d) { Node *cur=start; if(*d==*cur) { removeFirst();return; } cur=start->next; Node *prev=start,*del=NULL; while(cur!=NULL) { if(*cur==*d) { del=cur; prev->next=cur->next; delete del; noOfNodes--; break; } prev=prev->next; cur=cur->next; } } int getPosition(Node data) { int pos=0; Node *cur=(start); while(cur!=NULL) { pos++; if(*cur==data) { return pos; } cur=cur->next; } return -1;//not found } Node getNode(int pos) { if(pos<1) return -1;// not a valid position else if(pos>noOfNodes) return -1; // not a valid position Node *cur=(start); int curPos=0; while(cur!=NULL) { if(++curPos==pos) return *cur; cur=cur->next; } } void reverseList()//reverse the list { Node* cur=start->next; Node* d=NULL; Node* prev=start; while(cur!=NULL) { d=cur->next; cur->next=start; start=cur; prev->next=d; cur=d; } } void sortBubble() { Node *i=start,*j=start,*prev=NULL,*temp=NULL,*after=NULL; int count=noOfNodes-1;int icount=0; while(i->next!=NULL) { j=start; after=j->next; icount=0; while(++icount!=count) { if((*j)>(*after)) { temp=after->next; after->next=j; prev->next=j->next; j->next=temp; prev=after; after=j->next; } else{ prev=j; j=after; after=after->next; } } i=i->next; count--; } } void traverse() { Node *cur=(start); int c=0; while(cur!=NULL) { // cout<<"start"<<start; c++; cur->print(); cur=cur->next; } noOfNodes=c; } ~LList() { delete start; } }; int main() { int n; cin>>n; int d; LList list; Node *node; Node *temp=new Node(2123); for(int i=0;i<n;i++) { cin>>d; node=new Node(d); list.addAtLast(node); } list.addAtPos(temp,1); cout<<"traverse\n"; list.traverse(); temp=new Node(12); list.removeNode(temp); cout<<"12 removed"; list.traverse(); list.reverseList(); cout<<"\nreversed\n"; list.traverse(); cout<<"bubble sort\n"; list.sortBubble(); list.traverse(); getch(); delete node; return 0; }

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• PostSharp, Obfuscation, and IL

  - by simonc

  Aspect-oriented programming (AOP) is a relatively new programming paradigm. Originating at Xerox PARC in 1994, the paradigm was first made available for general-purpose development as an extension to Java in 2001. From there, it has quickly been adapted for use in all the common languages used today. In the .NET world, one of the primary AOP toolkits is PostSharp. Attributes and AOP Normally, attributes in .NET are entirely a metadata construct. Apart from a few special attributes in the .NET framework, they have no effect whatsoever on how a class or method executes within the CLR. Only by using reflection at runtime can you access any attributes declared on a type or type member. PostSharp changes this. By declaring a custom attribute that derives from PostSharp.Aspects.Aspect, applying it to types and type members, and running the resulting assembly through the PostSharp postprocessor, you can essentially declare 'clever' attributes that change the behaviour of whatever the aspect has been applied to at runtime. A simple example of this is logging. By declaring a TraceAttribute that derives from OnMethodBoundaryAspect, you can automatically log when a method has been executed: public class TraceAttribute : PostSharp.Aspects.OnMethodBoundaryAspect { public override void OnEntry(MethodExecutionArgs args) { MethodBase method = args.Method; System.Diagnostics.Trace.WriteLine( String.Format( "Entering {0}.{1}.", method.DeclaringType.FullName, method.Name)); } public override void OnExit(MethodExecutionArgs args) { MethodBase method = args.Method; System.Diagnostics.Trace.WriteLine( String.Format( "Leaving {0}.{1}.", method.DeclaringType.FullName, method.Name)); } } [Trace] public void MethodToLog() { ... } Now, whenever MethodToLog is executed, the aspect will automatically log entry and exit, without having to add the logging code to MethodToLog itself. PostSharp Performance Now this does introduce a performance overhead - as you can see, the aspect allows access to the MethodBase of the method the aspect has been applied to. If you were limited to C#, you would be forced to retrieve each MethodBase instance using Type.GetMethod(), matching on the method name and signature. This is slow. Fortunately, PostSharp is not limited to C#. It can use any instruction available in IL. And in IL, you can do some very neat things. Ldtoken C# allows you to get the Type object corresponding to a specific type name using the typeof operator: Type t = typeof(Random); The C# compiler compiles this operator to the following IL: ldtoken [mscorlib]System.Random call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle( valuetype [mscorlib]System.RuntimeTypeHandle) The ldtoken instruction obtains a special handle to a type called a RuntimeTypeHandle, and from that, the Type object can be obtained using GetTypeFromHandle. These are both relatively fast operations - no string lookup is required, only direct assembly and CLR constructs are used. However, a little-known feature is that ldtoken is not just limited to types; it can also get information on methods and fields, encapsulated in a RuntimeMethodHandle or RuntimeFieldHandle: // get a MethodBase for String.EndsWith(string) ldtoken method instance bool [mscorlib]System.String::EndsWith(string) call class [mscorlib]System.Reflection.MethodBase [mscorlib]System.Reflection.MethodBase::GetMethodFromHandle( valuetype [mscorlib]System.RuntimeMethodHandle) // get a FieldInfo for the String.Empty field ldtoken field string [mscorlib]System.String::Empty call class [mscorlib]System.Reflection.FieldInfo [mscorlib]System.Reflection.FieldInfo::GetFieldFromHandle( valuetype [mscorlib]System.RuntimeFieldHandle) These usages of ldtoken aren't usable from C# or VB, and aren't likely to be added anytime soon (Eric Lippert's done a blog post on the possibility of adding infoof, methodof or fieldof operators to C#). However, PostSharp deals directly with IL, and so can use ldtoken to get MethodBase objects quickly and cheaply, without having to resort to string lookups. The kicker However, there are problems. Because ldtoken for methods or fields isn't accessible from C# or VB, it hasn't been as well-tested as ldtoken for types. This has resulted in various obscure bugs in most versions of the CLR when dealing with ldtoken and methods, and specifically, generic methods and methods of generic types. This means that PostSharp was behaving incorrectly, or just plain crashing, when aspects were applied to methods that were generic in some way. So, PostSharp has to work around this. Without using the metadata tokens directly, the only way to get the MethodBase of generic methods is to use reflection: Type.GetMethod(), passing in the method name as a string along with information on the signature. Now, this works fine. It's slower than using ldtoken directly, but it works, and this only has to be done for generic methods. Unfortunately, this poses problems when the assembly is obfuscated. PostSharp and Obfuscation When using ldtoken, obfuscators don't affect how PostSharp operates. Because the ldtoken instruction directly references the type, method or field within the assembly, it is unaffected if the name of the object is changed by an obfuscator. However, the indirect loading used for generic methods was breaking, because that uses the name of the method when the assembly is put through the PostSharp postprocessor to lookup the MethodBase at runtime. If the name then changes, PostSharp can't find it anymore, and the assembly breaks. So, PostSharp needs to know about any changes an obfuscator does to an assembly. The way PostSharp does this is by adding another layer of indirection. When PostSharp obfuscation support is enabled, it includes an extra 'name table' resource in the assembly, consisting of a series of method & type names. When PostSharp needs to lookup a method using reflection, instead of encoding the method name directly, it looks up the method name at a fixed offset inside that name table: MethodBase genericMethod = typeof(ContainingClass).GetMethod(GetNameAtIndex(22)); PostSharp.NameTable resource: ... 20: get_Prop1 21: set_Prop1 22: DoFoo 23: GetWibble When the assembly is later processed by an obfuscator, the obfuscator can replace all the method and type names within the name table with their new name. That way, the reflection lookups performed by PostSharp will now use the new names, and everything will work as expected: MethodBase genericMethod = typeof(#kGy).GetMethod(GetNameAtIndex(22)); PostSharp.NameTable resource: ... 20: #kkA 21: #zAb 22: #EF5a 23: #2tg As you can see, this requires direct support by an obfuscator in order to perform these rewrites. Dotfuscator supports it, and now, starting with SmartAssembly 6.6.4, SmartAssembly does too. So, a relatively simple solution to a tricky problem, with some CLR bugs thrown in for good measure. You don't see those every day! Cross posted from Simple Talk.

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• LINQ – SequenceEqual() method

  - by nmarun

  I have been looking at LINQ extension methods and have blogged about what I learned from them in my blog space. Next in line is the SequenceEqual() method. Here’s the description about this method: “Determines whether two sequences are equal by comparing the elements by using the default equality comparer for their type.” Let’s play with some code: 1: int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; 2: // int[] numbersCopy = numbers; 3: int[] numbersCopy = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; 4:  5: Console.WriteLine(numbers.SequenceEqual(numbersCopy)); This gives an output of ‘True’ – basically compares each of the elements in the two arrays and returns true in this case. The result is same even if you uncomment line 2 and comment line 3 (I didn’t need to say that now did I?). So then what happens for custom types? For this, I created a Product class with the following definition: 1: class Product 2: { 3: public int ProductId { get; set; } 4: public string Name { get; set; } 5: public string Category { get; set; } 6: public DateTime MfgDate { get; set; } 7: public Status Status { get; set; } 8: } 9:  10: public enum Status 11: { 12: Active = 1, 13: InActive = 2, 14: OffShelf = 3, 15: } In my calling code, I’m just adding a few product items: 1: private static List<Product> GetProducts() 2: { 3: return new List<Product> 4: { 5: new Product 6: { 7: ProductId = 1, 8: Name = "Laptop", 9: Category = "Computer", 10: MfgDate = new DateTime(2003, 4, 3), 11: Status = Status.Active, 12: }, 13: new Product 14: { 15: ProductId = 2, 16: Name = "Compact Disc", 17: Category = "Water Sport", 18: MfgDate = new DateTime(2009, 12, 3), 19: Status = Status.InActive, 20: }, 21: new Product 22: { 23: ProductId = 3, 24: Name = "Floppy", 25: Category = "Computer", 26: MfgDate = new DateTime(1993, 3, 7), 27: Status = Status.OffShelf, 28: }, 29: }; 30: } Now for the actual check: 1: List<Product> products1 = GetProducts(); 2: List<Product> products2 = GetProducts(); 3:  4: Console.WriteLine(products1.SequenceEqual(products2)); This one returns ‘False’ and the reason is simple – this one checks for reference equality and the products in the both the lists get different ‘memory addresses’ (sounds like I’m talking in ‘C’). In order to modify this behavior and return a ‘True’ result, we need to modify the Product class as follows: 1: class Product : IEquatable<Product> 2: { 3: public int ProductId { get; set; } 4: public string Name { get; set; } 5: public string Category { get; set; } 6: public DateTime MfgDate { get; set; } 7: public Status Status { get; set; } 8:  9: public override bool Equals(object obj) 10: { 11: return Equals(obj as Product); 12: } 13:  14: public bool Equals(Product other) 15: { 16: //Check whether the compared object is null. 17: if (ReferenceEquals(other, null)) return false; 18:  19: //Check whether the compared object references the same data. 20: if (ReferenceEquals(this, other)) return true; 21:  22: //Check whether the products' properties are equal. 23: return ProductId.Equals(other.ProductId) 24: && Name.Equals(other.Name) 25: && Category.Equals(other.Category) 26: && MfgDate.Equals(other.MfgDate) 27: && Status.Equals(other.Status); 28: } 29:  30: // If Equals() returns true for a pair of objects 31: // then GetHashCode() must return the same value for these objects. 32: // read why in the following articles: 33: // http://geekswithblogs.net/akraus1/archive/2010/02/28/138234.aspx 34: // http://stackoverflow.com/questions/371328/why-is-it-important-to-override-gethashcode-when-equals-method-is-overriden-in-c 35: public override int GetHashCode() 36: { 37: //Get hash code for the ProductId field. 38: int hashProductId = ProductId.GetHashCode(); 39:  40: //Get hash code for the Name field if it is not null. 41: int hashName = Name == null ? 0 : Name.GetHashCode(); 42:  43: //Get hash code for the ProductId field. 44: int hashCategory = Category.GetHashCode(); 45:  46: //Get hash code for the ProductId field. 47: int hashMfgDate = MfgDate.GetHashCode(); 48:  49: //Get hash code for the ProductId field. 50: int hashStatus = Status.GetHashCode(); 51: //Calculate the hash code for the product. 52: return hashProductId ^ hashName ^ hashCategory & hashMfgDate & hashStatus; 53: } 54:  55: public static bool operator ==(Product a, Product b) 56: { 57: // Enable a == b for null references to return the right value 58: if (ReferenceEquals(a, b)) 59: { 60: return true; 61: } 62: // If one is null and the other not. Remember a==null will lead to Stackoverflow! 63: if (ReferenceEquals(a, null)) 64: { 65: return false; 66: } 67: return a.Equals((object)b); 68: } 69:  70: public static bool operator !=(Product a, Product b) 71: { 72: return !(a == b); 73: } 74: } Now THAT kinda looks overwhelming. But lets take one simple step at a time. Ok first thing you’ve noticed is that the class implements IEquatable<Product> interface – the key step towards achieving our goal. This interface provides us with an ‘Equals’ method to perform the test for equality with another Product object, in this case. This method is called in the following situations: when you do a ProductInstance.Equals(AnotherProductInstance) and when you perform actions like Contains<T>, IndexOf() or Remove() on your collection Coming to the Equals method defined line 14 onwards. The two ‘if’ blocks check for null and referential equality using the ReferenceEquals() method defined in the Object class. Line 23 is where I’m doing the actual check on the properties of the Product instances. This is what returns the ‘True’ for us when we run the application. I have also overridden the Object.Equals() method which calls the Equals() method of the interface. One thing to remember is that anytime you override the Equals() method, its’ a good practice to override the GetHashCode() method and overload the ‘==’ and the ‘!=’ operators. For detailed information on this, please read this and this. Since we’ve overloaded the operators as well, we get ‘True’ when we do actions like: 1: Console.WriteLine(products1.Contains(products2[0])); 2: Console.WriteLine(products1[0] == products2[0]); This completes the full circle on the SequenceEqual() method. See the code used in the article here.

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• asterisk/freeswitch in nat/no-nat setup

  - by pQd

  hi, my current setup - i use bunch of sip hard-phones around few offices. all devices have two sip accounts configured - one on internal sip proxy [for calls between the branches], another - at 3rd party voip providers [ since it's in different countries - those are different providers, but that's irrelevant ]. i was thinking about terminating sip calls on something like asterisk/freeswitch server and having all sip-devices log on just once to such server[s] - mostly to provide things like voicemail, groupcalls, redirections etc. it seems perfectly doable but there is one problem - i cannot find examples how to prepare for nat/no nat. for calls routed to from/to 3rd party voip operator - i'll need handling for nat/stun etc, but for handling of internal calls - i do not want any nat, all traffic should go via vpns to different branches. can you provide me some hints how to configure it? any tutorials? thanks!

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• What is needed to use anycast IPs?

  - by coredump

  So, there're a bunch of questions on SF about the uses and how anycast IPs are cool. My approach is something more practical. What specifically I need to have to use one of those addresses? Do I need to be an AS (Autonomous System)? If I want to use an Anycast IP on my internal network, is it possible? Do I need anything special with a registrar/operator(s) to use it? Basically, if I want to use an Anycast IP address, what exactly I need, from the equipment to configuration part.

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• Internet speed is suddenly slow only on my laptop, but it's normal in other devices

  - by Wael

  I have a TP-Link router connected to a ZTE modem, with 2 laptops, a tablet, 2 phones connected via the router's WiFi, and an additional desktop connected via ethernet to the router. Today, my laptop started to have a very slow connection to the internet, which at first I thought it was the operator's problem to find out later on that it works fine on other devices. I tried to connect directly via WiFi to the modem, but it was as slow. I cannot access facebook at all, google takes forever to do a search, and youtube barely works. The weird thing though, is that when youtube does work, the streaming is full speed. This happens also when I download a file! My browse is Firefox, but I used Chrome and IE9 with the same results. I work on Windows 7 Thanks for any advices.

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• Cleaning Up Unused Users and Groups (Ubuntu 10.10 Server)

  - by PhpMyCoder

  Hello experts, I'm very much a beginner when it comes to Ubuntu and I've been learning the ropes by diving in and writing a (backend-language independent) web app framework that relies on apache, some clever mod_rewrites, Ubuntu permissions, groups, and users. One thing that really annoys my inner clean-freak is that there are loads of users and groups that are created when Ubuntu is installed that are never used (Or so I think). Since I'm just running a simple web app server, I would like to know: What users/groups can I remove? Since you'll probably ask for it...here's a list of all the users on my box (excluding the ones I know that I need): root daemon bin sys sync man lp mail uucp proxy backup list irc gnats nobody libuuid syslog And a list of all of the groups: root daemon bin sys adm tty disk lp mail uucp man proxy kmem dialout fax voice cdrom floppy tape sudo audio dip backup operator list irc src gnats shadow utmp video sasl plugdev users nogroup libuuid crontab syslog fuse mlocate ssl-cert lpadmin sambashare admin

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• Accessing DHCP Client's vendor-encapsulated-options

  - by Jason Owen

  In the dhcpd.conf file for isc-dhcpd-V3.1.1, I have set up a vendor options space and defined several different options. I am able to use those definitions to send options from the server to the client in the vendor-encapsulated-options option (code 43). However, the client is also sending vendor options back to the server, in the same way, and I'd like to respond differently depending on the type and contents of the options. As far as I can tell, the the server isn't parsing the client's vendor-encapsulated-options at all - the option operator is just returning null. Is there a way to get the server to populate the options in the vendor space I've defined?

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• CUPS basic auth error through web interface

  - by Inaimathi

  I'm trying to configure CUPS to allow remote administration through the web interface. There's enough documentation out there that I can figure out what to change in my cupsd.conf (changing Listen localhost:631 to Port 631, and adding Allow @LOCAL to the /, /admin and /admin/conf sections). I'm now at the point where I can see the CUPS interface from another machine on the same network. The trouble is, when I try to Add Printer, I'm asked for a username and password, but my response is rejected even when I know I've gotten it right (I assume it's asking for the username and password of someone in the lpadmin group on the server machine; I've sshed in with credentials its rejecting, and the user I'm using has been added to the lpadmin group). If I disable auth outright, by changing DefaultAuthType Basic to DefaultAuthType None, I get an "Unauthorized" error instead of a password request when I try to Add Printer. What am I doing wrong? Is there a way of letting users from the local network to administer the print server through the CUPS web interface? EDIT: By request, my complete cupsd.conf (spoiler: minimally edited default config file that comes with the edition of CUPS from the Debian wheezy repos): LogLevel warn MaxLogSize 0 SystemGroup lpadmin Port 631 # Listen localhost:631 Listen /var/run/cups/cups.sock Browsing On BrowseOrder allow,deny BrowseAllow all BrowseLocalProtocols CUPS dnssd # DefaultAuthType Basic DefaultAuthType None WebInterface Yes <Location /> Order allow,deny Allow @LOCAL </Location> <Location /admin> Order allow,deny Allow @LOCAL </Location> <Location /admin/conf> AuthType Default Require user @SYSTEM Order allow,deny Allow @LOCAL </Location> # Set the default printer/job policies... <Policy default> # Job/subscription privacy... JobPrivateAccess default JobPrivateValues default SubscriptionPrivateAccess default SubscriptionPrivateValues default # Job-related operations must be done by the owner or an administrator... <Limit Create-Job Print-Job Print-URI Validate-Job> Order deny,allow </Limit> <Limit Send-Document Send-URI Hold-Job Release-Job Restart-Job Purge-Jobs Set-Job-Attributes Create-Job-Subscription Renew-Subscription Cancel-Subscription Get-Notifications Reprocess-Job Cancel-Current-Job Suspend-Current-Job Resume-Job Cancel-My-Jobs Close-Job CUPS-Move-Job CUPS-Get-Document> Require user @OWNER @SYSTEM Order deny,allow </Limit> # All administration operations require an administrator to authenticate... <Limit CUPS-Add-Modify-Printer CUPS-Delete-Printer CUPS-Add-Modify-Class CUPS-Delete-Class CUPS-Set-Default CUPS-Get-Devices> AuthType Default Require user @SYSTEM Order deny,allow </Limit> # All printer operations require a printer operator to authenticate... <Limit Pause-Printer Resume-Printer Enable-Printer Disable-Printer Pause-Printer-After-Current-Job Hold-New-Jobs Release-Held-New-Jobs Deactivate-Printer Activate-Printer Restart-Printer Shutdown-Printer Startup-Printer Promote-Job Schedule-Job-After Cancel-Jobs CUPS-Accept-Jobs CUPS-Reject-Jobs> AuthType Default Require user @SYSTEM Order deny,allow </Limit> # Only the owner or an administrator can cancel or authenticate a job... <Limit Cancel-Job CUPS-Authenticate-Job> Require user @OWNER @SYSTEM Order deny,allow </Limit> <Limit All> Order deny,allow </Limit> </Policy> # Set the authenticated printer/job policies... <Policy authenticated> # Job/subscription privacy... JobPrivateAccess default JobPrivateValues default SubscriptionPrivateAccess default SubscriptionPrivateValues default # Job-related operations must be done by the owner or an administrator... <Limit Create-Job Print-Job Print-URI Validate-Job> AuthType Default Order deny,allow </Limit> <Limit Send-Document Send-URI Hold-Job Release-Job Restart-Job Purge-Jobs Set-Job-Attributes Create-Job-Subscription Renew-Subscription Cancel-Subscription Get-Notifications Reprocess-Job Cancel-Current-Job Suspend-Current-Job Resume-Job Cancel-My-Jobs Close-Job CUPS-Move-Job CUPS-Get-Document> AuthType Default Require user @OWNER @SYSTEM Order deny,allow </Limit> # All administration operations require an administrator to authenticate... <Limit CUPS-Add-Modify-Printer CUPS-Delete-Printer CUPS-Add-Modify-Class CUPS-Delete-Class CUPS-Set-Default> AuthType Default Require user @SYSTEM Order deny,allow </Limit> # All printer operations require a printer operator to authenticate... <Limit Pause-Printer Resume-Printer Enable-Printer Disable-Printer Pause-Printer-After-Current-Job Hold-New-Jobs Release-Held-New-Jobs Deactivate-Printer Activate-Printer Restart-Printer Shutdown-Printer Startup-Printer Promote-Job Schedule-Job-After Cancel-Jobs CUPS-Accept-Jobs CUPS-Reject-Jobs> AuthType Default Require user @SYSTEM Order deny,allow </Limit> # Only the owner or an administrator can cancel or authenticate a job... <Limit Cancel-Job CUPS-Authenticate-Job> AuthType Default Require user @OWNER @SYSTEM Order deny,allow </Limit> <Limit All> Order deny,allow </Limit> </Policy>

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• =~ (equal-sign tilde) and m" ... " in .htaccess directive [closed]

  - by Lèse majesté

  I saw this bit of code on an old forum post: SSLRequire %{HTTP_HOST} =~ m"\.secure\.powweb\.com" And I was just wondering what the =~ and m" ... " meant. I've been searching online and in the Apache documentation for any mention of the equal-sign tilde operator, but I've found no mention of it. I know that some directives can take a tilde to use a regular expression, but I've never seen the m" ... " form used before. What exactly is that m" ... " for? Where else would you see this form?

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• Entering IT field with only hobby experience?

  - by EA Bisson

  I can build computers, install servers, network mac, linux, and windows, build servers, do support etc. I do all of this at home/for friends/for hobbies. I have worked with computers every day since I was in elementary school (commodore 64, windows 3.1 etc.). I have IT bachelors in administrative management (so basically nothing good). I am getting another bachelor's in server admin, including about 5 certifications. I am the IT go to gal at every position usually because I know more than the IT people and have better people skills. My job history is random: office admin, hair braider, disney ride operator, camp counselor etc. I found a job I want its a entry level specialist (server) position. What do I put on a resume?

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• Chrome shows "The site's security certificate is not trusted" error

  - by Emerald214

  From this morning I get this error whenever I access Google Docs and some websites. My system datetime is correct and I checked "Automatically from the Internet". My BIOS is OK. I cleared everything (cache, cookie, private data) in Chrome and restarted OS but nothing changes. How to fix it? Firefox works but Chrome has that problem. The site's security certificate is not trusted! You attempted to reach docs.google.com, but the server presented a certificate issued by an entity that is not trusted by your computer's operating system. This may mean that the server has generated its own security credentials, which Google Chrome cannot rely on for identity information, or an attacker may be trying to intercept your communications. You cannot proceed because the website operator has requested heightened security for this domain.

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• Chrome is reporting GMail has Invalid Server Certificate, how do I find out who's fiddling with my certs?

  - by chillitom

  Chrome is giving the following warning when ever I try and visit GMail or a bunch of other SSL sites. Invalid Server Certificate You attempted to reach mail.google.com, but the server presented an invalid certificate. You cannot proceed because the website operator has requested heightened security for this domain. This is the certificate the Chrome reports as invalid: -----BEGIN CERTIFICATE----- MIIDIjCCAougAwIBAgIQK59+5colpiUUIEeCdTqbuTANBgkqhkiG9w0BAQUFADBM MQswCQYDVQQGEwJaQTElMCMGA1UEChMcVGhhd3RlIENvbnN1bHRpbmcgKFB0eSkg THRkLjEWMBQGA1UEAxMNVGhhd3RlIFNHQyBDQTAeFw0xMTEwMjYwMDAwMDBaFw0x MzA5MzAyMzU5NTlaMGkxCzAJBgNVBAYTAlVTMRMwEQYDVQQIEwpDYWxpZm9ybmlh MRYwFAYDVQQHFA1Nb3VudGFpbiBWaWV3MRMwEQYDVQQKFApHb29nbGUgSW5jMRgw FgYDVQQDFA9tYWlsLmdvb2dsZS5jb20wgZ8wDQYJKoZIhvcNAQEBBQADgY0AMIGJ AoGBAK85FZho5JL+T0/xu/8NLrD+Jaq9aARnJ+psQ0ynbcvIj36B7ocmJRASVDOe qj2bj46Ss0sB4/lKKcMP/ay300yXKT9pVc9wgwSvLgRudNYPFwn+niAkJOPHaJys Eb2S5LIbCfICMrtVGy0WXzASI+JMSo3C2j/huL/3OrGGvvDFAgMBAAGjgecwgeQw DAYDVR0TAQH/BAIwADA2BgNVHR8ELzAtMCugKaAnhiVodHRwOi8vY3JsLnRoYXd0 ZS5jb20vVGhhd3RlU0dDQ0EuY3JsMCgGA1UdJQQhMB8GCCsGAQUFBwMBBggrBgEF BQcDAgYJYIZIAYb4QgQBMHIGCCsGAQUFBwEBBGYwZDAiBggrBgEFBQcwAYYWaHR0 cDovL29jc3AudGhhd3RlLmNvbTA+BggrBgEFBQcwAoYyaHR0cDovL3d3dy50aGF3 dGUuY29tL3JlcG9zaXRvcnkvVGhhd3RlX1NHQ19DQS5jcnQwDQYJKoZIhvcNAQEF BQADgYEANYARzVI+hCn7wSjhIOUCj19xZVgdYnJXPOZeJWHTy60i+NiBpOf0rnzZ wW2qkw1iB5/yZ0eZNDNPPQJ09IHWOAgh6OKh+gVBnJzJ+fPIo+4NpddQVF4vfXm3 fgp8tuIsqK7+lNfNFjBxBKqeecPStiSnJavwSI4vw6e7UN0Pz7A= -----END CERTIFICATE----- I think someone or something (proxy, anti-virus, browser extension) is snooping on my SSL traffic. How can I determine who/what is doing this?

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• dev_install failed on ARM chromebook

  - by user1027721

  I'm trying this guide for having access to emerge on chromeos. http://www.chromium.org/chromium-os/how-tos-and-troubleshooting/install-software-on-base-images Unfortunately I always got the same error which is $ sudo dev_install Starting installation of developer packages. First, we download the necessary files. Downloading https://commondatastorage.googleapis.com/chromeos-dev-installer/board/daisy/full-3.168.0.0/packages/app-misc/mime-types-8.tbz2 % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 100 127 100 127 0 0 252 0 --:--:-- --:--:-- --:--:-- 305 [: 184: -ne: unexpected operator Extracting /usr/local/portage/packages/app-misc/mime-types-8.tbz2 I think that it somehow returns a 404 everytime. Thanks for your help

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• Unexpected behavior in Bash

  - by cYrus

  From man bash: A simple command is a sequence of optional variable assignments followed by blank-separated words and redirections, and terminated by a control operator. The first word specifies the command to be executed, and is passed as argument zero. The remaining words are passed as arguments to the invoked command. So it's perfectly legal to write: foo=bar echo $foo but it doesn't work as I expect (it prints just a newline). It's quite strange to me since: $ foo=bar printenv foo=bar TERM=rxvt-unicode [...] Could someone please explain me where I'm doing wrong?

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• Odd behavior on Shift-{Esc,Fx}

  - by ??????? ???????????

  Sometimes, when changing between the modes in Vim, I forget to take my finger off the Shift key. This innocent mistake is probably part of the luggage carried over from other terminals, but I have never seen my input treated this way. After changing from command mode to input mode, if I hit the Esc key while the Shift key is down, Vim will display <9b (Control Sequence Introducer) instead of switching to the command mode. At least two work-arounds to this intended behavior are available on the mintty site (faq, issue). " Avoiding escape timeout issues in vim :let &t_ti.="\e[?7727h" :let &t_te.="\e[?7727l" :noremap <EscO[ <Esc :noremap! <EscO[ <Esc " Remap escape :imap <special <CSI <ESC My question is about the syntax and the meaning of the first solution. From the looks of it, it seems like t_ti is being assigned a literal value, but I'm not sure why the "c address-of" operator is required. I'm also not sure why there are two noremap statements.

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• BASH function not escaping control characters

  - by ehime

  Hey guys I have a function that I'm using to find stuff, but unfortunately anytime I pass it a control character ($intVal or testing : etc) it chokes. I was wondering what the fix was? I can understand that using $ or % or : etc in grep without escaping causes this issue, but since I'm passing it in by reference I'm not sure how to escape it... Anyway, here's the code. function ffind() { if [ $1 ] ; then find -type f | grep -ir '$1' * | grep -v '.svn' else echo "'$1' is not a valid resource" fi } Example(s): $ ffind $intVal '' is not a valid resource $ ffind "testing :" bash: [: testing: unary operator expected 'testing :' is not a valid resource

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• Power Pivot - Average time per item

  - by Username

  I'm trying to calculate on average, how long it takes to make each item. Here is the data table: Date Item Quantity Operator 01/01/2014 Item1 3 John 01/01/2014 Item2 5 John 02/01/2014 Item1 7 Bob 02/01/2014 Item2 4 John 03/01/2014 Item1 2 Bob 07/01/2014 Item2 3 John On 01/01/2014 John made 3 of Item 1 and 5 of Item 2. If we only had the first 2 rows we can guess that it takes 0.375 days to make Item 1 and 0.625 days to make Item 2. I want to be able to calculate this on average using all the data and taking in to account the operators obviously working on different items. Thank you

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• How to select all labeled messages in Gmail inbox?

  - by Tony

  I have dozens of labels and sub-labels and dozens of filters. I use the 'skip inbox' on a lot of filters but have many more that I want to see in the inbox before I archive them. It's easy to shift-select a few dozen at a time to archive when they are NOT separated by non-labeled mail. What I want to do is to be able to select all mail that has any label in the inbox and archive it with one click so that nothing but unlabeled mail is left in the inbox. This doesn't seem to be any different than what the Select Starred search except I can't find a wildcard search operator for labels.

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• Can not RDP to Win 2003 box or initiate remote restart

  - by Richard West

  I've got a Windows 2003 server that's at my remote data center. This morning I tried to connect to it via RDP, but the connection fails with the following error: This computer can't connect to the remote computer. Try connecting again. If the problem continues, contact the owner of the remote computer or your network administrator. I have also trying issuing a remote shutdown/restart command using the "shutdown -i" command from my local system. No error is reported, however the system does not reboot. This server runs SQL Server 2005 and it is still fully operational and responsive to queries. I can also remotely connect to the services control panel of the remote system. Is there anything that I can try to regain control of the system, short of having an operator in the data center do a hard reboot on the server for me?

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• AWS Elastic load balancer doesn't decrease instances from Alarm Trigger

  - by jchysk

  I have a load balancer that I created an auto-scaling-group and launch-config for. I created the auto-scaling-group with a min-size of 1 and max size of 20. I have a scaledown policy: as-put-scaling-policy SBMScaleDownPolicy --auto-scaling-group SBMAutoScaleGroup --adjustment=-1 --type ChangeInCapacity --cooldown 300 Then I set up an alarm: mon-put-metric-alarm SBMLowCPUAlarm --comparison-operator LessThanThreshold --evaluation-periods 1 --metric-name CPUUtilization --namespace "AWS/EC2" --period 600 --statistic Average --threshold 35 --alarm-actions arn:aws:autoscaling:us-east-1:policystuffhere:autoScalingGroupName/SBMAutoScaleGroup:policyName/SBMScaleDownPolicy --dimensions "AutoScalingGroupName=SBMAutoScaleGroup" When average CPU usage over 10 minutes is under 35, in CloudFront the alarm shows up as "In Alarm State" but doesn't decrease the number of instances. Also, if there's only one instance running it'll spin up another to 2 even if a scale up alarm isn't hit. It seems like the default value is just set to 2 somehow. How can I change this?

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• Problem reinstalling GRUB

  - by DisgruntledGoat

  I have a PC that dual-boots Ubuntu and Windows Vista. I recently reinstalled Windows Vista after some problems and now the bootloader's gone. I've been trying to follow this Ubuntu community guide but it's not working. I have Grub Legacy according to the first part (I installed Ubuntu 9.04 originally then upgraded). From the 9.04 LiveCD, I ran this: sudo grub-install --root-directory=/media/disk /dev/sda5 sda5 is the Ubuntu partition. I get this output: grub-probe: error: Cannot open `/boot/grub/device.map` [: 494: =: unexpected operator Installing GRUB to /dev/sda5 as (hd0,4)... Installation finished.No errors reported. This is the contents...(etc) (hd0) /dev/sda In the bit below, when I run setup (hd0) I get an error, "Error 17: Cannot mount selected partition" Little help?

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• See network computer description in Explorer

  - by John Gardeniers

  When viewing the list of network computers in Windows Explorer on a Win 7 machine there appears to be no way of readily seeing the description field, which makes that pretty well useless. I believe this problem started with Vista but I'm seeing it for the first time because I was fortunate enough to skip over Vista. We're currently rolling out Win 7 on new boxes and although I'm changing the naming system to something more sensible, the old boxes have names such as FWS01, FWS02, etc. Managing a network of computers with such names is made more difficult when you can't readily see who's machine each one is. Googling the problem brought up a workaround involving creating a shortcut on an XP machine and copying that to the Win 7 box but that's a long way from ideal. Is there some kind of hack that can be applied to machines, the operator of which needs to be able to see the description field?

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• Is the iPad in Europe totally unblocked?

  - by Mike

  One fast question: if I buy an iPad 3G in Europe will it work on other places without jailbreak? I ask this because I heard that, in Europe, iPads are not blocked to any telecom but I am not sure about that. On the other hand I am afraid do buy because I know that their cousins, iphones, are blocked to a specific telecom. Another question is regarding activation. As far as I remembered, my iPhone required me to do an activation step on iTunes and I remember it was also activated (or whatever) on the store (I remembered the salesman connected it to a computer and did some stuff before giving me the device). Is the iPad in europe totally free of operator? totally unblocked? thanks.

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