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  • Does anyone really understand how HFSC scheduling in Linux/BSD works?

    - by Mecki
    I read the original SIGCOMM '97 PostScript paper about HFSC, it is very technically, but I understand the basic concept. Instead of giving a linear service curve (as with pretty much every other scheduling algorithm), you can specify a convex or concave service curve and thus it is possible to decouple bandwidth and delay. However, even though this paper mentions to kind of scheduling algorithms being used (real-time and link-share), it always only mentions ONE curve per scheduling class (the decoupling is done by specifying this curve, only one curve is needed for that). Now HFSC has been implemented for BSD (OpenBSD, FreeBSD, etc.) using the ALTQ scheduling framework and it has been implemented Linux using the TC scheduling framework (part of iproute2). Both implementations added two additional service curves, that were NOT in the original paper! A real-time service curve and an upper-limit service curve. Again, please note that the original paper mentions two scheduling algorithms (real-time and link-share), but in that paper both work with one single service curve. There never have been two independent service curves for either one as you currently find in BSD and Linux. Even worse, some version of ALTQ seems to add an additional queue priority to HSFC (there is no such thing as priority in the original paper either). I found several BSD HowTo's mentioning this priority setting (even though the man page of the latest ALTQ release knows no such parameter for HSFC, so officially it does not even exist). This all makes the HFSC scheduling even more complex than the algorithm described in the original paper and there are tons of tutorials on the Internet that often contradict each other, one claiming the opposite of the other one. This is probably the main reason why nobody really seems to understand how HFSC scheduling really works. Before I can ask my questions, we need a sample setup of some kind. I'll use a very simple one as seen in the image below: Here are some questions I cannot answer because the tutorials contradict each other: What for do I need a real-time curve at all? Assuming A1, A2, B1, B2 are all 128 kbit/s link-share (no real-time curve for either one), then each of those will get 128 kbit/s if the root has 512 kbit/s to distribute (and A and B are both 256 kbit/s of course), right? Why would I additionally give A1 and B1 a real-time curve with 128 kbit/s? What would this be good for? To give those two a higher priority? According to original paper I can give them a higher priority by using a curve, that's what HFSC is all about after all. By giving both classes a curve of [256kbit/s 20ms 128kbit/s] both have twice the priority than A2 and B2 automatically (still only getting 128 kbit/s on average) Does the real-time bandwidth count towards the link-share bandwidth? E.g. if A1 and B1 both only have 64kbit/s real-time and 64kbit/s link-share bandwidth, does that mean once they are served 64kbit/s via real-time, their link-share requirement is satisfied as well (they might get excess bandwidth, but lets ignore that for a second) or does that mean they get another 64 kbit/s via link-share? So does each class has a bandwidth "requirement" of real-time plus link-share? Or does a class only have a higher requirement than the real-time curve if the link-share curve is higher than the real-time curve (current link-share requirement equals specified link-share requirement minus real-time bandwidth already provided to this class)? Is upper limit curve applied to real-time as well, only to link-share, or maybe to both? Some tutorials say one way, some say the other way. Some even claim upper-limit is the maximum for real-time bandwidth + link-share bandwidth? What is the truth? Assuming A2 and B2 are both 128 kbit/s, does it make any difference if A1 and B1 are 128 kbit/s link-share only, or 64 kbit/s real-time and 128 kbit/s link-share, and if so, what difference? If I use the seperate real-time curve to increase priorities of classes, why would I need "curves" at all? Why is not real-time a flat value and link-share also a flat value? Why are both curves? The need for curves is clear in the original paper, because there is only one attribute of that kind per class. But now, having three attributes (real-time, link-share, and upper-limit) what for do I still need curves on each one? Why would I want the curves shape (not average bandwidth, but their slopes) to be different for real-time and link-share traffic? According to the little documentation available, real-time curve values are totally ignored for inner classes (class A and B), they are only applied to leaf classes (A1, A2, B1, B2). If that is true, why does the ALTQ HFSC sample configuration (search for 3.3 Sample configuration) set real-time curves on inner classes and claims that those set the guaranteed rate of those inner classes? Isn't that completely pointless? (note: pshare sets the link-share curve in ALTQ and grate the real-time curve; you can see this in the paragraph above the sample configuration). Some tutorials say the sum of all real-time curves may not be higher than 80% of the line speed, others say it must not be higher than 70% of the line speed. Which one is right or are they maybe both wrong? One tutorial said you shall forget all the theory. No matter how things really work (schedulers and bandwidth distribution), imagine the three curves according to the following "simplified mind model": real-time is the guaranteed bandwidth that this class will always get. link-share is the bandwidth that this class wants to become fully satisfied, but satisfaction cannot be guaranteed. In case there is excess bandwidth, the class might even get offered more bandwidth than necessary to become satisfied, but it may never use more than upper-limit says. For all this to work, the sum of all real-time bandwidths may not be above xx% of the line speed (see question above, the percentage varies). Question: Is this more or less accurate or a total misunderstanding of HSFC? And if assumption above is really accurate, where is prioritization in that model? E.g. every class might have a real-time bandwidth (guaranteed), a link-share bandwidth (not guaranteed) and an maybe an upper-limit, but still some classes have higher priority needs than other classes. In that case I must still prioritize somehow, even among real-time traffic of those classes. Would I prioritize by the slope of the curves? And if so, which curve? The real-time curve? The link-share curve? The upper-limit curve? All of them? Would I give all of them the same slope or each a different one and how to find out the right slope? I still haven't lost hope that there exists at least a hand full of people in this world that really understood HFSC and are able to answer all these questions accurately. And doing so without contradicting each other in the answers would be really nice ;-)

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  • multiple ssh aliases is selecting wrong user when forwarding

    - by Chris Beck
    I'm following the dual identity procedure for bitbucket: I have 2 bitbucket accounts ccmcbeck and chrisbeck. The former is personal, the latter is work. On my local Mac, I have this in my ~/.ssh/config Host *.work.com User chris ForwardAgent yes IdentityFile ~/.ssh/work_dsa Host bitbucket-personal HostName bitbucket.org User ccmcbeck ForwardAgent no IdentityFile ~/.ssh/bitbucket_ccmcbeck_rsa Host bitbucket-work HostName bitbucket.org User chrisbeck ForwardAgent no IdentityFile ~/.ssh/bitbucket_chrisbeck_rsa On my local Mac I ssh -T all is good, I get: $ ssh -T git@bitbucket-personal logged in as ccmcbeck. $ ssh -T git@bitbucket-work logged in as chrisbeck. On my local Mac, the ssh version is OpenSSH_6.2p2, OSSLShim 0.9.8r 8 Dec 2011 When I ssh foo.work.com to my Linux box, I get: $ ssh-add -l 1024 ... /Users/chris/.ssh/work_dsa (DSA) 2048 ... /Users/chris/.ssh/bitbucket_ccmcbeck_rsa (RSA) 2048 ... /Users/chris/.ssh/bitbucket_chrisbeck_rsa (RSA) On foo.work.com, I also have this in my ~/.ssh/config Host bitbucket-personal HostName bitbucket.org User ccmcbeck ForwardAgent no IdentityFile ~/.ssh/bitbucket_ccmcbeck_rsa Host bitbucket-work HostName bitbucket.org User chrisbeck ForwardAgent no IdentityFile ~/.ssh/bitbucket_chrisbeck_rsa However, on foo.work.com when I ssh -T, it references the wrong User for git@bitbucket-work $ ssh -T git@bitbucket-personal logged in as ccmcbeck. $ ssh -T git@bitbucket-work logged in as ccmcbeck. On foo.work.com, the ssh version is OpenSSH_4.3p2, OpenSSL 0.9.8e-fips-rhel5 01 Jul 2008 Why is my configuration causing foo.work.com to reference the wrong User?

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  • Parallel processing slower than sequential?

    - by zebediah49
    EDIT: For anyone who stumbles upon this in the future: Imagemagick uses a MP library. It's faster to use available cores if they're around, but if you have parallel jobs, it's unhelpful. Do one of the following: do your jobs serially (with Imagemagick in parallel mode) set MAGICK_THREAD_LIMIT=1 for your invocation of the imagemagick binary in question. By making Imagemagick use only one thread, it slows down by 20-30% in my test cases, but meant I could run one job per core without issues, for a significant net increase in performance. Original question: While converting some images using ImageMagick, I noticed a somewhat strange effect. Using xargs was significantly slower than a standard for loop. Since xargs limited to a single process should act like a for loop, I tested that, and found it to be about the same. Thus, we have this demonstration. Quad core (AMD Athalon X4, 2.6GHz) Working entirely on a tempfs (16g ram total; no swap) No other major loads Results: /media/ramdisk/img$ time for f in *.bmp; do echo $f ${f%bmp}png; done | xargs -n 2 -P 1 convert -auto-level real 0m3.784s user 0m2.240s sys 0m0.230s /media/ramdisk/img$ time for f in *.bmp; do echo $f ${f%bmp}png; done | xargs -n 2 -P 2 convert -auto-level real 0m9.097s user 0m28.020s sys 0m0.910s /media/ramdisk/img$ time for f in *.bmp; do echo $f ${f%bmp}png; done | xargs -n 2 -P 10 convert -auto-level real 0m9.844s user 0m33.200s sys 0m1.270s Can anyone think of a reason why running two instances of this program takes more than twice as long in real time, and more than ten times as long in processor time to complete the same task? After that initial hit, more processes do not seem to have as significant of an effect. I thought it might have to do with disk seeking, so I did that test entirely in ram. Could it have something to do with how Convert works, and having more than one copy at once means it cannot use processor cache as efficiently or something? EDIT: When done with 1000x 769KB files, performance is as expected. Interesting. /media/ramdisk/img$ time for f in *.bmp; do echo $f ${f%bmp}png; done | xargs -n 2 -P 1 convert -auto-level real 3m37.679s user 5m6.980s sys 0m6.340s /media/ramdisk/img$ time for f in *.bmp; do echo $f ${f%bmp}png; done | xargs -n 2 -P 1 convert -auto-level real 3m37.152s user 5m6.140s sys 0m6.530s /media/ramdisk/img$ time for f in *.bmp; do echo $f ${f%bmp}png; done | xargs -n 2 -P 2 convert -auto-level real 2m7.578s user 5m35.410s sys 0m6.050s /media/ramdisk/img$ time for f in *.bmp; do echo $f ${f%bmp}png; done | xargs -n 2 -P 4 convert -auto-level real 1m36.959s user 5m48.900s sys 0m6.350s /media/ramdisk/img$ time for f in *.bmp; do echo $f ${f%bmp}png; done | xargs -n 2 -P 10 convert -auto-level real 1m36.392s user 5m54.840s sys 0m5.650s

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  • A New Threat To Web Applications: Connection String Parameter Pollution (CSPP)

    - by eric.maurice
    Hi, this is Shaomin Wang. I am a security analyst in Oracle's Security Alerts Group. My primary responsibility is to evaluate the security vulnerabilities reported externally by security researchers on Oracle Fusion Middleware and to ensure timely resolution through the Critical Patch Update. Today, I am going to talk about a serious type of attack: Connection String Parameter Pollution (CSPP). Earlier this year, at the Black Hat DC 2010 Conference, two Spanish security researchers, Jose Palazon and Chema Alonso, unveiled a new class of security vulnerabilities, which target insecure dynamic connections between web applications and databases. The attack called Connection String Parameter Pollution (CSPP) exploits specifically the semicolon delimited database connection strings that are constructed dynamically based on the user inputs from web applications. CSPP, if carried out successfully, can be used to steal user identities and hijack web credentials. CSPP is a high risk attack because of the relative ease with which it can be carried out (low access complexity) and the potential results it can have (high impact). In today's blog, we are going to first look at what connection strings are and then review the different ways connection string injections can be leveraged by malicious hackers. We will then discuss how CSPP differs from traditional connection string injection, and the measures organizations can take to prevent this kind of attacks. In web applications, a connection string is a set of values that specifies information to connect to backend data repositories, in most cases, databases. The connection string is passed to a provider or driver to initiate a connection. Vendors or manufacturers write their own providers for different databases. Since there are many different providers and each provider has multiple ways to make a connection, there are many different ways to write a connection string. Here are some examples of connection strings from Oracle Data Provider for .Net/ODP.Net: Oracle Data Provider for .Net / ODP.Net; Manufacturer: Oracle; Type: .NET Framework Class Library: - Using TNS Data Source = orcl; User ID = myUsername; Password = myPassword; - Using integrated security Data Source = orcl; Integrated Security = SSPI; - Using the Easy Connect Naming Method Data Source = username/password@//myserver:1521/my.server.com - Specifying Pooling parameters Data Source=myOracleDB; User Id=myUsername; Password=myPassword; Min Pool Size=10; Connection Lifetime=120; Connection Timeout=60; Incr Pool Size=5; Decr Pool Size=2; There are many variations of the connection strings, but the majority of connection strings are key value pairs delimited by semicolons. Attacks on connection strings are not new (see for example, this SANS White Paper on Securing SQL Connection String). Connection strings are vulnerable to injection attacks when dynamic string concatenation is used to build connection strings based on user input. When the user input is not validated or filtered, and malicious text or characters are not properly escaped, an attacker can potentially access sensitive data or resources. For a number of years now, vendors, including Oracle, have created connection string builder class tools to help developers generate valid connection strings and potentially prevent this kind of vulnerability. Unfortunately, not all application developers use these utilities because they are not aware of the danger posed by this kind of attacks. So how are Connection String parameter Pollution (CSPP) attacks different from traditional Connection String Injection attacks? First, let's look at what parameter pollution attacks are. Parameter pollution is a technique, which typically involves appending repeating parameters to the request strings to attack the receiving end. Much of the public attention around parameter pollution was initiated as a result of a presentation on HTTP Parameter Pollution attacks by Stefano Di Paola and Luca Carettoni delivered at the 2009 Appsec OWASP Conference in Poland. In HTTP Parameter Pollution attacks, an attacker submits additional parameters in HTTP GET/POST to a web application, and if these parameters have the same name as an existing parameter, the web application may react in different ways depends on how the web application and web server deal with multiple parameters with the same name. When applied to connections strings, the rule for the majority of database providers is the "last one wins" algorithm. If a KEYWORD=VALUE pair occurs more than once in the connection string, the value associated with the LAST occurrence is used. This opens the door to some serious attacks. By way of example, in a web application, a user enters username and password; a subsequent connection string is generated to connect to the back end database. Data Source = myDataSource; Initial Catalog = db; Integrated Security = no; User ID = myUsername; Password = XXX; In the password field, if the attacker enters "xxx; Integrated Security = true", the connection string becomes, Data Source = myDataSource; Initial Catalog = db; Integrated Security = no; User ID = myUsername; Password = XXX; Intergrated Security = true; Under the "last one wins" principle, the web application will then try to connect to the database using the operating system account under which the application is running to bypass normal authentication. CSPP poses serious risks for unprepared organizations. It can be particularly dangerous if an Enterprise Systems Management web front-end is compromised, because attackers can then gain access to control panels to configure databases, systems accounts, etc. Fortunately, organizations can take steps to prevent this kind of attacks. CSPP falls into the Injection category of attacks like Cross Site Scripting or SQL Injection, which are made possible when inputs from users are not properly escaped or sanitized. Escaping is a technique used to ensure that characters (mostly from user inputs) are treated as data, not as characters, that is relevant to the interpreter's parser. Software developers need to become aware of the danger of these attacks and learn about the defenses mechanism they need to introduce in their code. As well, software vendors need to provide templates or classes to facilitate coding and eliminate developers' guesswork for protecting against such vulnerabilities. Oracle has introduced the OracleConnectionStringBuilder class in Oracle Data Provider for .NET. Using this class, developers can employ a configuration file to provide the connection string and/or dynamically set the values through key/value pairs. It makes creating connection strings less error-prone and easier to manager, and ultimately using the OracleConnectionStringBuilder class provides better security against injection into connection strings. For More Information: - The OracleConnectionStringBuilder is located at http://download.oracle.com/docs/cd/B28359_01/win.111/b28375/OracleConnectionStringBuilderClass.htm - Oracle has developed a publicly available course on preventing SQL Injections. The Server Technologies Curriculum course "Defending Against SQL Injection Attacks!" is located at http://st-curriculum.oracle.com/tutorial/SQLInjection/index.htm - The OWASP web site also provides a number of useful resources. It is located at http://www.owasp.org/index.php/Main_Page

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  • Finding the groups of a user in WLS with OPSS

    - by user12587121
    How to find the group memberships for a user from a web application running in Weblogic server ?  This is useful for building up the profile of the user for security purposes for example. WLS as a container offers an identity store service which applications can access to query and manage identities known to the container.  This article for example shows how to recover the groups of the current user, but how can we find the same information for an arbitrary user ? It is the Oracle Platform for Securtiy Services (OPSS) that looks after the identity store in WLS and so it is in the OPSS APIs that we can find the way to recover this information. This is explained in the following documents.  Starting from the FMW 11.1.1.5 book list, with the Security Overview document we can see how WLS uses OPSS: Proceeding to the more detailed Application Security document, we find this list of useful references for security in FMW. We can follow on into the User/Role API javadoc. The Application Security document explains how to ensure that the identity store is configured appropriately to allow the OPSS APIs to work.  We must verify that the jps-config.xml file where the application  is deployed has it's identity store configured--look for the following elements in that file: <serviceProvider type="IDENTITY_STORE" name="idstore.ldap.provider" class="oracle.security.jps.internal.idstore.ldap.LdapIdentityStoreProvider">             <description>LDAP-based IdentityStore Provider</description>  </serviceProvider> <serviceInstance name="idstore.ldap" provider="idstore.ldap.provider">             <property name="idstore.config.provider" value="oracle.security.jps.wls.internal.idstore.WlsLdapIdStoreConfigProvider"/>             <property name="CONNECTION_POOL_CLASS" value="oracle.security.idm.providers.stdldap.JNDIPool"/></serviceInstance> <serviceInstanceRef ref="idstore.ldap"/> The document contains a code sample for using the identity store here. Once we have the identity store reference we can recover the user's group memberships using the RoleManager interface:             RoleManager roleManager = idStore.getRoleManager();            SearchResponse grantedRoles = null;            try{                System.out.println("Retrieving granted WLS roles for user " + userPrincipal.getName());                grantedRoles = roleManager.getGrantedRoles(userPrincipal, false);                while( grantedRoles.hasNext()){                      Identity id = grantedRoles.next();                      System.out.println("  disp name=" + id.getDisplayName() +                                  " Name=" + id.getName() +                                  " Principal=" + id.getPrincipal() +                                  "Unique Name=" + id.getUniqueName());                     // Here, we must use WLSGroupImpl() to build the Principal otherwise                     // OES does not recognize it.                      retSubject.getPrincipals().add(new WLSGroupImpl(id.getPrincipal().getName()));                 }            }catch(Exception ex) {                System.out.println("Error getting roles for user " + ex.getMessage());                ex.printStackTrace();            }        }catch(Exception ex) {            System.out.println("OESGateway: Got exception instantiating idstore reference");        } This small JDeveloper project has a simple servlet that executes a request for the user weblogic's roles on executing a get on the default URL.  The full code to recover a user's goups is in the getSubjectWithRoles() method in the project.

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  • What's the best way of handling permissions for apache2's user www-data in /var/www ?

    - by gyaresu
    Has anyone got a nice solution for handling files in /var/www/ ? We're running Name Based Virtual Hosts and the apache2 user is 'www-data' We've got two regular users & root. So when messing with files in /var/www ,rather than having to... chown -R www-data:www-data ...all the time, what's a good way of handling this? Supplementary question. How hardcore do you then go on permissions? This one has always been a problem in collaborative development environments. Cheers.

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  • What is the easiest/simplest way to change the HD on a Linux server?

    - by ArmlessJohn
    Hello. I have a machine running Ubuntu Server that has been presenting some HD-related problems. Instead of reinstalling and reconfiguring everything (and to save time) we'd like to copy everything from the current hard drive to a new one and start using it. We only have a single hard drive with a main partition and a swap partition. What tools or methods would you recommend for replacing a hard drive with minimum difficulty and chance of problems? Thank you.

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  • Why am I seeing MailSlot Browse messages on unrouted ports of my Linux box?

    - by nmichaels
    I have a Linux box (Debian squeeze) with several NICs. The ones of interest are: eth3 - my main link to the network (dhcp on 10.20.30.0/24) eth0 - the first connection to my test network (static: 192.168.1.2) eth4 - the second connection to my test network (static: 192.168.1.1) My routing table looks like this: $ sudo route Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 10.20.30.0 * 255.255.255.0 U 0 0 0 eth3 default 10.20.30.254 0.0.0.0 UG 0 0 0 eth3 I have the 2 test net ports connected to each other with a crossover cable and an instance of wireshark running on each port. Every once in a while, I'll see a packet like the following show up. Who could be doing this, and how do I convince them to stop? I do have Samba running on the machine (for a cifs mount) but don't see why it would be sending packets out to unrouted ports. I had a Windows VM running in VMWare Client and thought that might be causing it, but it still happens without it. What I want is totally silent interfaces so I can run some tests with Scapy over them.

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  • X11 tunnelling through SSH from Fedora 3 server to Windows Vista client fails to work.

    - by MiffTheFox
    Okay, I've tried using Xming and PuTTY, as well as Cygwin/X and Cygwin ssh, and it is not working. I've been able to run X applications locally, so it's not a client-side X problem. I've connected to the server using ssh -X user@server and ended up with this: local-user@client: ~$ ssh -X user@server user@server's password: Last login: Sun Jul 19 15:26:46 2009 from 192.168.100.147 [user@server ~]$ xclock & [1] 27770 [user@server ~]$ Error: Can't open display: localhost:10.0 [1]+ Exit 1 xclock [user@server ~]$ [user@server ~]$ Here's the relevant snippet of my sshd_config #AllowTcpForwarding yes #GatewayPorts no #X11Forwarding no X11Forwarding yes X11DisplayOffset 10 X11UseLocalhost yes I can't seem to find ssh_config on the client-side. /etc/ssh doesn't exist.

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  • How to set up an FTP user on UBUNTU 9 server using vsftpd utility?

    - by Pavel
    Hi guys. I'm kinda new to this so bear with me. I've set up a server and now I need to create ftp user for it. I'm doing this by typing: useradd pavel passwd pavel And then I'm running iptables -I INPUT 1 -p tcp --dport 21 -j ACCEPT iptables-save > /etc/iptables.rules in order to open ftp ports and lastly, I'm changing the usermod by: usermod -s /bin/sh pavel So now tell me - what I'm doing wrong here? I just want to connect using FTP protocol. Please help...

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  • Why is my filesystem being mounted read-only in linux?

    - by Tim
    I am trying to set up a small linux system based on Gentoo on a VirtualBox machine, as a step towards deploying the same system onto a low-spec Single Board Computer. For some reason, my filesystem is being mounted read-only. In my /etc/fstab, I have: /dev/sda1 / ext3 defaults 0 0 none /proc proc defaults 0 0 none /sys sysfs defaults 0 0 none /dev/shm tmpfs defaults 0 0 However, once booted /proc/mounts shows rootfs / rootfs rw 0 0 /dev/root / ext3 ro,relatime,errors=continue,barrier=0,data=writeback 0 0 proc /proc proc rw,nosuid,nodev,noexec,relatime 0 0 sysfs /sys sysfs rw,nosuid,nodev,noexec,relatime 0 0 udev /dev tmpfs rw,nosuid,relatime,size=10240k,mode=755 0 0 devpts /dev/pts devpts rw,nosuid,noexec,relatime,gid=5,mode=620 0 0 none /dev/shm tmpfs rw,relatime 0 0 usbfs /proc/bus/usb usbfs rw,nosuid,noexec,relatime,devgid=85,devmode=664 0 0 binfmt_misc /proc/sys/fs/binfmt_misc binfmt_misc rw,nosuid,nodev,noexec,relatime 0 0 (the above may contain errors: there's no practical way to copy and paste) The partition at /dev/hda1 is clearly being mounted OK, since I can read all the data, but it's not being mounted as described in fstab. How might I go about diagnosing / resolving this? Edit: I can remount with mount -o remount,rw / and it works as expected, except that /proc/mounts reports /dev/root mounted at / rather than /dev/sda1 as I'd expect. If I try to remount with mount -a I get mount: none already mounted or /sys busy mount: according to mtab, sysfs is already mounted on /sys Edit 2: I resolved the problem with mount -a (the same error was occuring during startup, it turned out) by changing the sysfs and proc lines to proc /proc proc [...] sysfs /sys sysfs [...] Now mount -a doesn't complain, but it doesn't result in a read-write root partition. mount -o remount / does cause the root partition to be remounted, however.

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  • Understanding the Linux boot process, subsystem initialization, & udev rules?

    - by quack quixote
    I'm creating UDEV rules for automounting external drives on a headless server, much in the same way as Gnome-VFS does automounting during a user session. I'm concerned with the rule's behavior at boot-time. There's a good chance one of these drives will be connected during a boot, and I'd prefer any connected drives get mounted in the right place. The drives might be either USB or Firewire, and they are mounted from a shell script fired off by UDEV on detecting an "add". Here are my questions: When UDEV runs the mount for these devices at boot, will the system be ready to mount it? Or will the script get triggered too early? If it's too early, what's a good way for a script to tell that the system isn't ready yet (so sleep a while before checking again)? The UDEV rule matches ACTION=="add". Does this event even fire at system boot?

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  • Simple Linux program that takes any HTTP/HTTPS request and returns a single page?

    - by ultrasawblade
    I have a Linux box operating as router. There's a NIC that's connected to the internet (WAN), a NIC connected to an 8-port GbE switch (LAN), and a NIC connected to a Linksys wireless N-router (WLAN). Routing between everything is working perfectly. I have security completely disabled on the wireless router, but the WLAN NIC is firewalled such that it will only accept DNS queries and PPTP VPN connections. Currently HTTP/HTTPS traffic and everything else is blocked. I would like to run something that listens on port 80/443 of the WLAN NIC, and, for non VPN'ed connections, given any HTTP/HTTPS request it will return a single webpage saying "Unauthenticated" and explain how to sign into the VPN. A transparent proxy seems to be what I need, but my searches all seem to direct me to Squid, which is already running on my server and seems overkill for this simple task. Is there a simpler, lightweight program out there that does just this or should I just suck it up and run two instances of Squid (or figure out how to configure it)? Or, is this entire VPN thing I'm doing complete nonsense and I should just enable encryption on the wireless router?

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  • What permissions / ownership to set on PHP Sessions Folder when running FastCGI / PHP-FPM (as user "nobody")?

    - by Professor Frink
    I'm having trouble getting a number of scripts running because PHP-FPM can't write to my session folder: "2009/10/01 23:54:07 [error] 17830#0: *24 FastCGI sent in stderr: "PHP Warning: Unknown: open(/var/lib/php/session/sess_cskfq4godj4ka2a637i5lq41o5, O_RDWR) failed: Permission denied (13) in Unknown on line 0 PHP Warning: Unknown: Failed to write session data (files). Please verify that the current setting of session.save_path is correct (/var/lib/php/session) in Unknown on line 0" while reading upstream" Obviously this is a permission issue; my session folder's owner/group is the webserver's user, NGINX. PHP-FPM runs as nobody though, and hence adding it to the nginx group is not so trivial. A temporary solution is to set the permissions of /var/lib/php/session to 777 - I have a feeling that's not the "best practice" though. What is the best practice when you need to assign a daemon write access to a folder, but it is running as nobody ?

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  • In Linux, when I use the PS command, why do I see multiple lines for www-data?

    - by johnlai2004
    I have a LAMP server that uses ubuntu 9.10, apache2, mysql5 and php5. When I login as root through the shell, I run a "ps aux" command and see something like the following www-data 3151 0.1 4.3 220024 31032 ? S 12:22 0:00 /usr/sbin/apache2 -k start www-data 3153 0.2 3.6 214776 26020 ? S 12:22 0:01 /usr/sbin/apache2 -k start www-data 3162 0.3 5.1 225060 36920 ? S 12:26 0:01 /usr/sbin/apache2 -k start www-data 3163 0.1 4.1 218872 29664 ? S 12:26 0:00 /usr/sbin/apache2 -k start How come I see multiple lines for www-data? Does each line represent an actual user on my website? I run into memory issues at times, so I'm trying to determine if these www-data statistics are related.

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  • What is the best graphical terminal/console for Linux?

    - by bgy
    Well, I'm often tired of the basic functionalities of terminal provided as is when installing a new distribution. What is the best console in a graphical mode? For now, all I want to is: Tabs management Easy copy/paste (^C/^V support) UTF-8 support Should be available for both KDE/Gnome environnement Please be argumentative, don't answer with 'my favorite is' only. Try to tell me why and which features it offers.

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  • Reverse bash console text flow

    - by radman
    Hi, This is a bit of a weird question and I'm not sure that there is any easy answer to it but I am very interested in finding a solution. So when I work on a linux machine via a console I find that I am constantly staring at the bottom of the screen, as once you have executed a bunch of commands text fills toward the bottom. Now I find that this is decidedly not good for my neck and it would be far better if instead of scrolling to the bottom, the text would scroll to the top instead. So does anyone out there know if there is a way to reverse the direction text appears in a console? (note that i am aware of the clear command) Example: default behaviour user@machine:~$ command 1 user@machine:~$ command 2 user@machine:~$ command 3 user@machine:~$ __active_prompt__ desired behaviour user@machine:~$ __active_prompt__ user@machine:~$ command 3 user@machine:~$ command 2 user@machine:~$ command 1 Running Kubuntu 10.04 using Konsole I realise this is an odd question, thanks for any help.

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  • Does MySQL have some kind of DoS protection or per-user query limit?

    - by Ghostrider
    I'm a bit at a loss. I'm running a MySQL database that's roughly 1GB data in indices combined on a dedicated Linux server. DB version is '5.0.89-community'. Configuration is controlled via cPanel. PHP actually runs elsewhere on a shared hosting. IP addresses are static and don't change. Access from remote IP address is properly configured. Website gets around 10K hits per day with each hit generating a a database query. Some of these queries are expensive (~1 sec execution time). All is fine and well until at some point DB server starts refusing connections from the client, claiming that specific user can't access the server from that IP. Resetting the server will always fix the problem for a day or two and then the same thing happens. There are some other DBs on that server, some of which are hit pretty hard on occasion but constantnly. One of the apps maintains several persistent connections since it does couple of updates per minute. Though I don't think it's related. What's driving me mad is that I can't figure out why server would start refusing connections. There is nothing in the logs. This server is a hosted dedicated server so hosting company created the OS image and I didn't write or go over every line of configuration. I'd do it but I'm at a loss as to where start looking. Any advice is appreciated.

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  • Is there any way to force my Linux box to always boot up with a self-assigned IP address?

    - by Jeremy Friesner
    This is perhaps an unusual request: I'm trying to get a Debian Linux box to always give itself a self-assigned IP address (i.e. 169.254.x.y) on boot. In particular, I want it to do that even when there is a DHCP server present on the LAN. That is, it should not request an IP address from the DHCP server. From what I can see in the "man interfaces" text, there is an option for "manual", and an option for "dhcp". Manual assignment won't do, since I need multiple boxes to work on the same LAN without requiring any manual configuration... and "dhcp" does what I want, but only if there is no DHCP server on the LAN. (A requirement is that the functionality of these boxes should not be affected by the presence or absence of a DHCP server). Is there a trick that I can use to get this behavior? EDIT: By "no manual configuration", I mean that I should be able to take this box (headless) to any LAN anywhere, plug in the Ethernet cable, and have it do its thing. I shouldn't have to ssh to the box and edit files to get it working each time it is moved to a different LAN.

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  • Backup solution to backup terabytes and lots of static files on linux server?

    - by user28679
    Which backup tool or solution would you use to backup terabytes and lots of files on a production linux server ? Note that the files are all different and almost never modified, and usage is mostly adding files, so data volume is today 3TB growing all the time at around +15GB/day. Please do not reply rsync. Basic unix tools are not enough, rsync does not keep history, rdiff-backup miserably fails from time to time and screw the history. Moreover these are all file based backup, which put a lot of IOwait just to browse directories and query stat(). But i guess, except R1Soft CDP, there is no way around that. We tried R1Soft CDP backup, which is block level backup, and it proved good and efficient for all our other servers, but systematically fails on the server with 3 terabytes and gazillions of files. That is already more than 2 months that the engineers of R1Soft and datacenter are playing a hot ball game... and still no backup except regular rsync We never tried big commercial solutions, except R1Soft CDP since it was provided as an optional service by the datacented hosting our servers.

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  • Run Active Directory Admin Center as another user

    - by dunxd
    I am trying to run Active Directory Admin Center (dsac.exe) on Windows 7 as another user by means of creating a shortcut, rather than having to Shift+Right click and specify the user. On Windows XP I could create a runas shortcut like this (forget for a moment that dsac.exe does not exist in Windows XP): runas /user:DOMAIN\user dsac.exe When I run this on Windows 7, the cmd style windows pops up and asks for the password for DOMAIN\user, but I get the following message: Attempting to start dsac.exe as user "DOMAIN\user" ... RUNAS ERROR: Unable to run - dsac.exe 740: The requested operation requires elevation. How do I get Windows 7 to automatically run dsac.exe as a specified user? I'm happy to fill in a password prompt for the specified user, but would be even happier if there was a solution that cached the password, so I didn't have to enter it more than once a day.

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  • What to do after a fresh Linux install in a production server?

    - by Rhyuk
    I havent had previous experience with the 'serious' IT scene. At work I've been handed a server that will host an application and MYSQL (I will install and configure everything), this will be a productive server. Soon I will be installing RHEL5 to it but I would like to know like, if you get a new production server, what would be the first 5 things you would do after you do a fresh Linux install? (configuration/security/reliability wise) EDIT: Added more information regarding the server enviroment and server roles: -The server will be inside my company's intranet/firewall. -The server will receive files (GBs) in binary code from another internal server. The application installed in this server is in charge of "translating" all that binary into human readable input. Server will get queried to get this information. -Only 2-3(max) users will be logging in. -(2) 145GB HDs in RAID1 for the OS and (2) 600GB HDs in RAID1 also for data. I mean, I know I may not get the perfect guideline. But at least something thats better than leaving everything on default.

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