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  • Prevent Linux from processing incoming ICMP Host unreachable packets

    - by bbc
    I have a test setup with one host on a network (10.1.0.0/16) talking via TCP to another one on another network (10.2.0.0/16) and a gateway in the middle. Sometimes, the TCP connection is lost and while scanning the trace (pcap), I looks like it's because of just one ICMP Host unreachable message sent by the gateway to 10.1.0.1 at some point. 10.1.0.1 then sends a TCP RST to 10.2.0.1. In my opinion, the gateway (pfSense) is broken or not configured correctly but anyway, for testing purposes, I'd like to block this kind of ICMP on the host (10.1.0.1) before it has an influence on my TCP connection (or does it? I'm not even sure). I've tried iptables: iptables -I INPUT -i eth0 -p icmp --icmp-type host-unreachable -j DROP but while it does a good job at preventing userpace applications like ping from receiving these ICMP messages, my TCP connection still comes to an end when the alleged "killer ICMP packet" is sent by the gateway. Am I right about how it is processed? If yes, then what can I do to achieve my goal?

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  • Linux security: The dangers of executing malignant code as a standard user

    - by AndreasT
    Slipping some (non-root) user a piece of malignant code that he or she executes might be considered as one of the highest security breaches possible. (The only higher I can see is actually accessing the root user) What can an attacker effectively do when he/she gets a standard, (let's say a normal Ubuntu user) to execute code? Where would an attacker go from there? What would that piece of code do? Let's say that the user is not stupid enough to be lured into entering the root/sudo password into a form/program she doesn't know. Only software from trusted sources is installed. The way I see it there is not really much one could do, is there? Addition: I partially ask this because I am thinking of granting some people shell (non-root) access to my server. They should be able to have normal access to programs. I want them to be able to compile programs with gcc. So there will definitely be arbitrary code run in user-space...

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  • Configuration tools for multiple monitors for X / Linux

    - by richard
    I have Ubuntu 10.04 running gnome and two monitors. I am wondering if a can get a better multi-monitor configuration tool. The one I have, gnome-display-properties, has too many problems, including: when I swapped my monitors over, the narrower one now on the left. There is a width calculation error, such that I have a virtual monitor the width of the wide-monitor on the narrow-monitor and part of the wide monitor. And a virtual narrow-monitor on the remainder of the wide-monitor. I would like: nobugs. to be able to select which is primary monitor. to have multiple configurations. configurations to be automatically selected based on which monitors are attached. configurations to be cycled (reliably) when display mode key is pressed. when a display is deactivated, for windows to migrate to remaining monitors. option to not change display resolution when mirroring, but to use side/top blanking bars to pad out screen.

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  • How to distill / rasterize a PDF in Linux

    - by Sampo
    We have a printer at our office that prints PDF files from a USB stick. It prints most files okay, but it has problems with some, especially ones generated with Latex. Some PDFs it simply refuses to print, some PDFs it prints with courier-type font, and some it prints fine except for equations. I'm looking for a way to "distill" PDFs into a dead-sure format to print. Either by simplifying / normalizing the PDF to the point that any renderer will render it correctly, or by simply making each page a 600dpi raster image in the PDF. (I could split the PDF into individual raster images and combine them manually, but I want something scriptable.) The output file size doesn't matter, as long as it's sure to print, has A4 paper size (or the original) and 300~600dpi resolution.

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  • Linux as a router for public networks

    - by nixnotwin
    My ISP had given me a /30 network. Later, when I wanted more public ips, I requested for a /29 network. I was told to keep using my earlier /30 network on the interface which is facing ISP, and the newly given /29 network should be used on the other interface which connects to my NAT router and servers. This is what I got from the isp: WAN IP: 179.xxx.4.128/30 CUSTOMER IP : 179.xxx.4.130 ISP GATEWAY IP:179.xxx.4.129 SUBNET : 255.255.255.252 LAN IPS: 179.xxx.139.224/29 GATEWAY IP :179.xxx.139.225 SUBNET : 255.255.255.248 I have a Ubuntu pc which has two interfaces. So I am planning to do the following: eth0 will be given 179.xxx.4.130/30 gateway 179.xxx.4.129 eth1 will be given 179.xxx.139.225/29 And I will have the following in the /etc/sysctl.conf: net.ipv4.ip_forward=1 These will be iptables rules: iptables -A FORWARD -i eth0 -o eth1 -j ACCEPT iptables -A FORWARD -i eth1 -o eth0 -j ACCEPT My clients which have the ips 179.xxx.139.226/29 and 179.xxx.139.227/29 will be made to use 179.xxx.139.225/29 as gateway. Will this configuration work for me? Any comments? If it works, what iptables rules can I use to have a bit of security? P.S. Both networks are non-private and there is no NATing.

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  • Backup linux to ftp server

    - by Alakdae
    What do you use for backups to ftp server? I've tried the setup with Amanda and virtual tapes on the ftp server mounted with Curlftpfs and I'm not satisfied with it. I just don't feel confident about Amanda. Also I cannot use anything that uses rsync on the ftp mounted filesystem because it only creates the directories and doesn't create files as it cannot execute "mkstemp". I've been thinking about Bacula but I can't find any good HOWTO for it.

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  • Restricting access to a subdirectory on linux

    - by David
    I'm looking for a way to make a directory accessible only to its parent directories. That is, suppose you have two directories, A and B, at the same level in the file hierarchy. Now suppose that you have a directory A' which is a subdirectory of A. I'd like to enforce that A is able to access the contents of A' but B is not. My problem is that I'd like to use a library (directory A) which builds on top of a legacy version of another library (directory A'). At the same time, I want to be able to use the newest version of this legacy library (directory B). I want to make sure that people aren't somehow using library A and linking against new library B by enforcing that library A must use library A'. I could just link A against library B, but then I'm risking compatibility.

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  • Unable to list contents/remove directory (linux ext3)

    - by RedKrieg
    System is CentOS5 x86_64, completely up to date. I've got a folder that can't be listed (ls just hangs, eating memory until it is killed). The directory size is nearly 500k: root@server [/home/user/public_html/domain.com/wp-content/uploads/2010/03]# stat . File: `.' Size: 458752 Blocks: 904 IO Block: 4096 directory Device: 812h/2066d Inode: 44499071 Links: 2 Access: (0755/drwxr-xr-x) Uid: ( 3292/ user) Gid: ( 3287/ user) Access: 2012-06-29 17:31:47.000000000 -0400 Modify: 2012-10-23 14:41:58.000000000 -0400 Change: 2012-10-23 14:41:58.000000000 -0400 I can see the file names if I use ls -1f, but it just repeats the same 48 files ad infinitum, all of which have non-ascii characters somewhere in the file name: La-critic\363-al-servicio-la-privacidad-300x160.jpg When I try to access the files (say to copy them or remove them) I get messages like the following: lstat("/home/user/public_html/domain.com/wp-content/uploads/2010/03/Sebast\355an-Pi\361era-el-balc\363n-150x120.jpg", 0x7fff364c52c0) = -1 ENOENT (No such file or directory) I tried altering the code found on this man page and modified the code to call unlink for each file. I get the same ENOENT error from the unlink call: unlink("/home/user/public_html/domain.com/wp-content/uploads/2010/03/Marca-naci\363n-Madrid-150x120.jpg") = -1 ENOENT (No such file or directory) I also straced a "touch", grabbed the syscalls it makes and replicated them, then tried to unlink the resulting file by name. This works fine, but the folder still contains an entry by the same name after the operation completes and the program runs for an arbitrarily long time (strace output ended up at 20GB after 5 minutes and I stopped the process). I'm stumped on this one, I'd really prefer not to have to take this production machine (hundreds of customers) offline to fsck the filesystem, but I'm leaning toward that being the only option at this point. If anyone's had success using other methods for removing files (by inode number, I can get those with the getdents code) I'd love to hear them. (Yes, I've tried find . -inum <inode> -exec rm -fv {} \; and it still has the problem with unlink returning ENOENT) For those interested, here's the diff between that man page's code and mine. I didn't bother with error checking on mallocs, etc because I'm lazy and this is a one-off: root@server [~]# diff -u listdir-orig.c listdir.c --- listdir-orig.c 2012-10-23 15:10:02.000000000 -0400 +++ listdir.c 2012-10-23 14:59:47.000000000 -0400 @@ -6,6 +6,7 @@ #include <stdlib.h> #include <sys/stat.h> #include <sys/syscall.h> +#include <string.h> #define handle_error(msg) \ do { perror(msg); exit(EXIT_FAILURE); } while (0) @@ -17,7 +18,7 @@ char d_name[]; }; -#define BUF_SIZE 1024 +#define BUF_SIZE 1024*1024*5 int main(int argc, char *argv[]) { @@ -26,11 +27,16 @@ struct linux_dirent *d; int bpos; char d_type; + int deleted; + int file_descriptor; fd = open(argc > 1 ? argv[1] : ".", O_RDONLY | O_DIRECTORY); if (fd == -1) handle_error("open"); + char* full_path; + char* fd_path; + for ( ; ; ) { nread = syscall(SYS_getdents, fd, buf, BUF_SIZE); if (nread == -1) @@ -55,7 +61,24 @@ printf("%4d %10lld %s\n", d->d_reclen, (long long) d->d_off, (char *) d->d_name); bpos += d->d_reclen; + if ( d_type == DT_REG ) + { + full_path = malloc(strlen((char *) d->d_name) + strlen(argv[1]) + 2); //One for the /, one for the \0 + strcpy(full_path, argv[1]); + strcat(full_path, (char *) d->d_name); + + //We're going to try to "touch" the file. + //file_descriptor = open(full_path, O_WRONLY|O_CREAT|O_NOCTTY|O_NONBLOCK, 0666); + //fd_path = malloc(32); //Lazy, only really needs 16 + //sprintf(fd_path, "/proc/self/fd/%d", file_descriptor); + //utimes(fd_path, NULL); + //close(file_descriptor); + deleted = unlink(full_path); + if ( deleted == -1 ) printf("Error unlinking file\n"); + break; //Break on first try + } } + break; //Break on first try } exit(EXIT_SUCCESS);

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  • Installing softare on Linux

    - by Dimen Shaw
    I'm trying to install the GMP package on Redhat 4, x86_64. The package can only be installed using make, which is not available and should be installed with apt-get/yum, but I don't have either one of them. I tried installing them using rpm, but they each require lots of dependencies themselves, which although finite in amount seem like a VERY tedious job to do. Any help on how I should go about solving this?

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  • Lost Linux root password - Recovery mode and init=/bin/bash fail

    - by Albeit
    I lost/forgot the root password to a server sitting beside me and am trying to reset it. I would rather not have to wipe and re-install or use a Live CD (server is running Ubuntu Server 12.04). What I've tried so far... 1) Boot into "Recovery mode" from Grub2 boot menu then drop into root shell prompt. I am prompted to "Give root password for maintenance". No-go. 2) Change the boot parameters for the main boot option to include "rw" and "init=/bin/bash". When I then boot with Ctrl-X, the screen goes black, and nothing happens (I've waited five minutes). init=/bin/sh and init=/bin/static-sh both do the same thing, while init=/sbin/init boots as normal. Is there anything else I can try to reset the root password? Thank you!

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  • Looking for a Linux stream ripper that can be scheduled

    - by Anthony D
    I have an MP3 stream I want to schedule a recording of. I can do it using wget to a file, its just a straight mp3 stream. However I'd like to use a command line stream ripper that will do a better job. Any one know of one? Update 1 WGET is grabbing whatever part of the stream it comes in on. This may not really be the start of a frame in the MP3 file. Also, wget is not really schedule ready. I experimented with starting it with a cron job, then killing it later, this produced a file that didn't really start and stop where I wanted.

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  • Linux file copy with ETA?

    - by bobby
    I'm copying a large amount of files between disks. There's approximately 16 GB of data. I'd like to see progress information, and even an estimated time of completion from the command line. Any advice?

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  • Linux foxboard network monitor

    - by het.oosten
    I want to use a Foxboard a simple network monitor for multiple routers (all routers are connected to the internet). Foxboard is a mini pc with an embedded version of Debian. My idea is to use multiple virtual network devices like this: eth0 192.168.2.10 eth0:1 192.168.3.10 eth0:2 192.168.4.10 I found a nice Python script to ping an external host here (the solution from Ryan Cox): http://stackoverflow.com/questions/316866/ping-a-site-in-python Is it possible to configure Debian to use eth0 when I ping www.site-a.com and eth0:1 when I ping www.site-b.com?

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  • Adding local users / passwords on Kerberized Linux box

    - by Brian
    Right now if I try to add a non-system user not in the university's Kerberos realm I am prompted for a Kerberos password anyway. Obviously there is no password to be entered, so I just press enter and see: passwd: Authentication token manipulation error passwd: password unchanged Typing passwd newuser has the same issue with the same message. I tried using pwconv in the hopes that only a shadow entry was needed, but it changed nothing. I want to be able to add a local user not in the realm and give them a local password without being bothered about Kerberos. I am on Ubuntu 10.04. Here are my /etc/pam.d/common-* files (the defaults that Ubuntu's pam-auth-update package generates): account # here are the per-package modules (the "Primary" block) account [success=1 new_authtok_reqd=done default=ignore] pam_unix.so # here's the fallback if no module succeeds account requisite pam_deny.so # prime the stack with a positive return value if there isn't one already; # this avoids us returning an error just because nothing sets a success code # since the modules above will each just jump around account required pam_permit.so # and here are more per-package modules (the "Additional" block) account required pam_krb5.so minimum_uid=1000 # end of pam-auth-update config auth # here are the per-package modules (the "Primary" block) auth [success=2 default=ignore] pam_krb5.so minimum_uid=1000 auth [success=1 default=ignore] pam_unix.so nullok_secure try_first_pass # here's the fallback if no module succeeds auth requisite pam_deny.so # prime the stack with a positive return value if there isn't one already; # this avoids us returning an error just because nothing sets a success code # since the modules above will each just jump around auth required pam_permit.so # and here are more per-package modules (the "Additional" block) # end of pam-auth-update config password # here are the per-package modules (the "Primary" block) password requisite pam_krb5.so minimum_uid=1000 password [success=1 default=ignore] pam_unix.so obscure use_authtok try_first_pass sha512 # here's the fallback if no module succeeds password requisite pam_deny.so # prime the stack with a positive return value if there isn't one already; # this avoids us returning an error just because nothing sets a success code # since the modules above will each just jump around password required pam_permit.so # and here are more per-package modules (the "Additional" block) # end of pam-auth-update config session # here are the per-package modules (the "Primary" block) session [default=1] pam_permit.so # here's the fallback if no module succeeds session requisite pam_deny.so # prime the stack with a positive return value if there isn't one already; # this avoids us returning an error just because nothing sets a success code # since the modules above will each just jump around session required pam_permit.so # and here are more per-package modules (the "Additional" block) session optional pam_krb5.so minimum_uid=1000 session required pam_unix.so # end of pam-auth-update config

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  • Tuning Linux + HAProxy

    - by react
    I'm currently rolling out HAProxy on Centos 6 which will send requests to some Apache HTTPD servers and I'm having issues with performance. I've spent the last couple of days googling and still can't seem to get past 10k/sec connections consistently when benchmarking (sometimes I do get 30k/sec though). I've pinned the IRQ's of the TX/RX queues for both the internal and external NICS to separate CPU cores and made sure HAProxy is pinned to it's own core. I've also made the following adjustments to sysctl.conf: # Max open file descriptors fs.file-max = 331287 # TCP Tuning net.ipv4.tcp_tw_reuse = 1 net.ipv4.ip_local_port_range = 1024 65023 net.ipv4.tcp_max_syn_backlog = 10240 net.ipv4.tcp_max_tw_buckets = 400000 net.ipv4.tcp_max_orphans = 60000 net.ipv4.tcp_synack_retries = 3 net.core.somaxconn = 40000 net.ipv4.tcp_rmem = 4096 8192 16384 net.ipv4.tcp_wmem = 4096 8192 16384 net.ipv4.tcp_mem = 65536 98304 131072 net.core.netdev_max_backlog = 40000 net.ipv4.tcp_tw_reuse = 1 If I use AB to hit the a webserver directly I easily get 30k/s connections. If I stop the webservers and use AB to hit HAProxy then I get 30k/s connections but obviously it's useless. I've also disabled iptables for now since I read that nf_conntrack can slow everything down, no change. I've also disabled the irqbalance service. The fact that I can hit each individual device with 30k/s makes me believe the tuning of the servers is OK and that it must be some HAProxy config? Here's the config which I've built from reading tuning articles, etc http://pastebin.com/zsCyAtgU The server is a dual Xeon CPU E5-2620 (6 cores) with 32GB of RAM. Running Centos 6.2 x64. The private and public interfaces are on separate NICS. Anyone have any ideas? Thanks.

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  • copy files created in one folder to multiple other folders on linux

    - by Keith
    I'm looking for a way to copy photos that are uploaded to one folder to many other folders and visa versa. Example: a photo is uploaded to folder 1, it is then copied to folders 2-5. And if a photo is uploaded to folder 2 it is copied to folders 1 and 3-5. I'm running CentOS 5. All of these folders are on the same server. I came across another post on here that talked about incron, but that type of programming is over my head.

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  • Linux: Tool to monitor every process, execute-command, shortly, monitor what's happening at the moment

    - by Bevor
    Hello, due to a freeze problem of my Ubuntu 10.10 (it is not isolatable) I though about logging every executable of the kernel somehow in any file to see what happens last when a freeze occures the next time to not lose valuable information. I found acct but this is obviously not what I'm looking for. Actually it logs just user commands and those things. I need something which logs in a much "deeper" level. The best would be some kind of script which records every interrupt. Does anybody know some tool like that?

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  • Linux Directory Access Problem: Permission Denied """In Root"""

    - by RBA
    Hi, When login through root on HP-tru Unix server, I am trying to access a directory, it is saying "Permission Denied".. Also, an sh file is also not able to execute through same root access.. I have checked the permission of the directory as well as for sh file through ls-ltr.. It is also fine.. Root System rwx-rwx-rwx-- What could be the possible cause, and how to correct it.. Thanks.

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  • Linux Log Viewer with Web interface

    - by user180039
    I have been asked at work to find a solution to one of our problems. We have several logs that customers need access to, because we don't want to give them direct access to the folder/share we are looking to implement a simple Web based solution that permits customers to login see a list of files they have permissions to and download the file. It would need to be able to setup permissions so User01 can see file01 and file03 and User02 can see file04 and file06, optimally all the files would be under the same folder, so permissions are based on files rather then based on folders. Anyone got any ideas Many Thanks

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  • Conditional `mount` in Linux: dev or nfs

    - by o_O Tync
    I have a mount point — let it be /media/question — and two possible devices: a physical HDD and a remote NFS folder. Sometimes I plug the device in physically, in other cases I mount it via NFS. Is there a way to specify both of them in fstab so that executing mount /media/question will preferably choose physical volume, and when it's not available — NFS?

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