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Questions tagged [linux]

Linux is the generic term for a UNIX-like open source operating system based on the Linux kernel.

8
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718 views

Is it possible to do multiseat the systemd way with one graphic card / two heads?

I would like to setup a multi-seat configuration using Ubuntu Xenial 16.04. After some researches, it seems the way to do now is by systemd through "loginctl" calls. (saw here for example). Before ...
7
votes
0answers
114 views

Write arbitrary attribute into ENV from LDAP upon successful PAM authentication

Is it possible during the authentication phase of pam_ldap to map an arbitrary LDAP attribute of the user's record into the resulting user's environment? The specifics of my situation, in case you ...
6
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0answers
1k views

CentOS 6 local update repository and security updates

I know that official CentOS 6 (even 7) update repositories does not provide security information. The consequence is thatyum-plugin-security plugin and yum check-update --security command does not ...
6
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0answers
1k views

ZFS cannot import : I/O error

I experienced an error in my ZFS machine. This may have happend after I lost power to my server, but I can not tell for sure. My ZFS Pool Gewuerzglas with RAIDZ-1 is no longer willing to import. I ...
6
votes
0answers
418 views

What ZFS file structure to use for zfs-root linux system?

In ZFS, you can build your filesystem hiearchy to include different fs-attributes per filesystem. For insance, compression in one area, no-exec/suid in others, noatime. For example, a HOWTO for ...
5
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0answers
195 views

How can I track down why the rpm DB on my servers keeps getting corrupted?

Running Centos 7 (various versions) The rpm DB on my servers keeps getting corrupted. It seems like every few weeks I have to do an rpm rebuild on a server or two. Where should I look to see what ...
5
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0answers
196 views

How to debug failed checksums/flipped bits in TCP packets?

A web application we maintain recently encountered a very weird problem: three out of four virtual machines on two physical hosts had trouble connecting to the server of our payment provider via HTTPS....
5
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0answers
523 views

Why very slow / no directory caching with SSHFS?

I have the below in /etc/fstab and when I cd ~/dat0 and then do anything in there e.g. tab complete, it takes 10 seconds every time. I.e. it doesn't cache anything. Is there something that can be ...
5
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0answers
3k views

Jenkins on Docker - Free Swap Space 0

I've noticed that my master node on Jenkins shows free swap space: 0 B So I added a swap file as described here. But this has no effect. What am I doing wrong?
5
votes
0answers
3k views

Wrong filename encoding/decoding when downloading recursively with wget

I'm downloading files from a remote directory recursively using wget and whoever created the folders and files, used special characters such as è or Ó, when I download a single specificating the full ...
5
votes
0answers
1k views

TCP congestion collapse

I am experiencing suboptimal performance on an EC2 instance connecting to an RDS instance. This particular instance was built before VPC's existed, so all the traffic is flowing through a single ...
5
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0answers
12k views

ActiveMQ - “Cannot send, channel has already failed” every 2 seconds?

ActiveMQ 5.7.0 CentOS release 6.3 java version "1.6.0_26" Application server: Tomcat In the activemq.log, I'm seeing this exception every 2 seconds: 2013-11-05 13:00:52,374 | DEBUG | Transport ...
5
votes
0answers
4k views

NAT64 configuration with tayga on Debian 6

I'm trying to implement NAT64 with tayga on my server and came to a point where I'm not sure how to proceed. My server is connected via one IPv4 address and one /64 IPv6 address block to the internet....
4
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0answers
45 views

Why does the same Java service use up to 4x the RAM when running 1 core vs 2 cores

I have an Ubuntu 18.04 VM image that runs a Java 8-based server process. When running on a single core EC2 t2.small instance (2GB RAM) it starts with an RSS of 432M. Running the exact same server ...
4
votes
0answers
310 views

Change default certificate signing algorithm in ssh-keygen

Presently, OpenSSH 7.8 (Fedora 28/Arch) is unable to negotiate with a OpenSSH 7.4 (CentOS 7) server utilizing a certificate signed key, as described in a bug filed on redhat's bugzilla. OpenSSH ...
4
votes
0answers
85 views

How long is an (accepted) ICMP redirect observed for, and how can I shorten that time?

If a Linux host receives and accepts an ICMP redirect (accept_redirects=1 on the interface in question), how long is this route being cached for and observed? Can I lower that time? I am asking ...
4
votes
0answers
599 views

mdadm marks hdd faulty even though it's in pristine health?

I have my custom NAS configured to spin down drives after 20 minutes of idle. Just now I checked /proc/mdstat and noticed a drive was marked as failed, however SMART shows the drive to be in very ...
4
votes
0answers
3k views

Sane value for net.ipv4.tcp_max_syn_backlog in sysctl.conf

I'm tuning sysctl.conf. According to an optimization guide on linode's website, the following is a sane value to set in sysctl.conf: net.ipv4.tcp_max_syn_backlog = 3240000 However, the same value ...
4
votes
0answers
726 views

Getting to enforcing google safe search using CNAME with unbound and nsd?

I am trying to implement this using Unbound and Nsd: https://support.google.com/websearch/answer/186669?hl=en To force SafeSearch for your network, you’ll need to update your DNS. configuration. ...
4
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0answers
162 views

The strangest docker fault I've ever seen

I am using Docker with docker-mailserver on one of my servers. Very strange trouble appeared after migrating some services from legacy Debian Jessie server to Ubuntu 16.04 LTS server. Parameters of ...
4
votes
0answers
155 views

Any limit on initcwnd?

We are trying to decrease the initial latency on TCP connections to our servers. In some test we found that when we download a file below 15587 bytes the total downloading time (apache benchmark total)...
4
votes
0answers
218 views

Programatically (with syscall) invalidate NFS lookupcache

I have a process that relies on detecting file creation on an NFS server. Usually it works fine, but there's been a few minor glitches recently, due to caching and an NFS rename operation. We've ...
4
votes
0answers
581 views

Auditd in a PCI-DSS-compliant Linux cluster

I'm familiar with some of the more common ways of configuring a Linux server to be compliant with PCI-DSS 3.2, at least to the requirements of SAQ A. A common concern is requirement 8.5 which ...
4
votes
0answers
124 views

Bind notifies on DNS views

I have configured two Cent OS based DNS servers one for master and one for slave with internal and external views for a domain. The problem is that i get notifies and automatic zone updates when i ...
4
votes
0answers
127 views

Block incoming traffic in bonding mode when primary interface is down

My server running on latest kernel (4.4.6) has configured a bond device (bond0) with two enslaved interfaces eth0, wlan0 with primary interface eth0. cat /proc/net/bonding/bond0 Ethernet Channel ...
4
votes
0answers
982 views

Linux max. value for vm.max_map_count

I'm planning to increase significantly the default value of 65k max mappings; let's say multiply by 10. Assuming we have enough memory on the machine is there anything I should take care of doing that?...
4
votes
0answers
3k views

OpenVPN - OpenVZ - Multicast and how to enable it

Good day all My application makes primary use of Multicast packets on ip = 224.8.0.1 I have tested over normal Wifi/Ethernet and hosted networks, which are all good. Problem: My OpenVZ server ...
4
votes
0answers
140 views

NGINX Worker Process, Burst Read Speed to only 1918kb/s

I am running an NGINX/1.8 server on Centos6.6 with multiple worker_processes, however while observing iotop I notice they burst up to 1918kb/s Read speed and rarely if at all pass that limit. I want ...
4
votes
0answers
825 views

detecting whether GPUs are accessible before running nvidia-smi during boot to create dev files

In the past, I've successfully configured Ubuntu systems containing NVIDIA GPUs to launch nvidia-smi in the background from within /etc/rc.local during the system boot to create the requisite /dev/...
4
votes
0answers
326 views

Heroku and socket.io out of memory

I have a setup with websockets on heroku and every now and then i get a flurry of messages like this: 06:24.591694+00:00 heroku router - - at=error code=H15 desc="Idle connection" method=GET path="/...
4
votes
0answers
1k views

TCP Window Scaling Problem over MPLS

After extensive troubleshooting why the TCP speed over an MPLS circuit is slow in one direction, I figured out that by adjusting the TCP window size the situation improved a lot. Maybe you can tell me ...
4
votes
0answers
2k views

TCP connection stuck in SYN_RECV state despite ACK received

My client and server are both internal machines. tcpdump on both client and server show all three parts of handshake are communicated, however netstat on server shows SYN_RECV, and on client shows ...
4
votes
0answers
1k views

Adaptec pm80xx Driver Drops Drives Randomly

I'm building a ZFS NAS using an Adaptec ASA-71605H HBA on Ubuntu 12.04.4. Modern Linux kernels ship with the open-source version of the required pm80xx kernel module. Adaptec provides a driver for ...
4
votes
0answers
1k views

TCP connections in FIN-WAIT-2 state on linux not timing out according to tcp_fin_timeout

We run a service with lots of embedded devices in the field, their tcp stack is a bit buggy and sometimes does not close connections properly, resulting in some connections being stuck in FIN-WAIT-2 ...
4
votes
0answers
650 views

snmp MIB-TCP::tcp not showing any usage

I am trying to configure MRTG on all of my servers for making a network weathermap, this requires running SNMP which MRTG gets the information from. So, I installed it on two servers the exact same ...
4
votes
0answers
4k views

ProFTPd/FTPS issue: unable to accept TLS connection: received EOF that violates protocol

It took some time while I tried to find solution over the net. Nothing helped. The story: I have Ubuntu 10.10 (Amazon EC2 instance). ProFTPD Version 1.3.2e (latest via apt-get). I changed nothing on ...
4
votes
0answers
984 views

How do I configure OpenSwan to allow pure IPsec (not L2TP) connections from an iPhone?

Similar to this question, I want to configure an IPsec server on Linux which will accept connections from the iPhone. However, unlike the other question, I want to be able to test with pre-shared keys ...
4
votes
0answers
4k views

how to tune NFS client on MacOS to get Linux like performance?

I have a NFS server running Linux and exporting a couple of shares. Both Linux and MacOS clients connect to the server, and while with the Linux clients I get ~ 75MB/s write speed, the MacOS clients ...
3
votes
0answers
67 views

Is there any way to get an AD bound linux system to mount home directories from a Windows server?

We've been experimenting with integrating linux systems into what is largely a Windows domain, with a Windows-based Active Directory server. After considerable trial and error, we have successfully ...
3
votes
0answers
343 views

How to make a RAID disk light blink (on Linux)?

I have a RAID10 hot-swap disk that is about to fail (according to smartctl -a /dev/sdc. The disk is mounted in a rack 4U server). Unfortunately, the disks are not marked, so I'd like to get the disk ...
3
votes
0answers
40 views

Network access stalls for some time on centos7 + zfs + samba installation

I have storage server with CentOS7 with 4 HDDs running on raidz (Raid 5). I access the files on it via samba. When I copy files from it or watch movies sometimes the reading from samba is blocked for ...
3
votes
0answers
281 views

Postfix forwarding - SPF issues - Sender rewrite

When using Postfix virtual alias maps to forward email to another domain, is it possible to have Postfix re-write the sender address exclusively for forwards to avoid SPF rejection at the final ...
3
votes
0answers
88 views

Does an ESX hypervisor report stolen time correctly to linux guests

I have a bunch of debian 8 guests running on an esxi 6 hypervisor. top seems to always report 0 for its steal time counter. Is the stolen time reporting supposed to work when linux runs on esxi ...
3
votes
0answers
1k views

Postgresql fails to start with no such file or directory error?

I was juggling Postgresql versions and I think I shot myself in the foot during the renaming of something. I have 9.3 and 9.4 installed on an Ubuntu 14.04 station, and I wanted to go back to 9.3 so I ...
3
votes
0answers
132 views

Matrix Synapse matrix-appservice-irc messages only travel from IRC to Matrix

My irc bridge has connected the rooms i wanted, except messages are only passed from irc to matrix! Also the matrix[m] users are not appearing in the irc chatroom. Here are my configs: $ cat config....
3
votes
0answers
76 views

Convert VM (redhat virtualization 3.5) to a physical server

I have a virtual machine running on red hat virtualization 3.5, i need to convert that VM to a physical server. (mainly due to a performance issue) my volume groups as follows NAME ...
3
votes
0answers
1k views

How to correctly prevent auto-assembly of RAID arrays on Ubuntu 16.04?

I'm trying to stop mdadm from automatically assembling RAID arrays when I attach disks. I had a solution that worked on Ubuntu 14.04, but it doesn't work on 16.04. I've found a thing that works for ...
3
votes
0answers
405 views

I'm trying to solve extremely high disk IO wait times. Can you tell me what this iotop output should have me look at?

Total DISK READ : 526.37 K/s | Total DISK WRITE : 111.99 K/s Actual DISK READ: 526.37 K/s | Actual DISK WRITE: 89.59 K/s PID PRIO USER DISK READ DISK WRITE SWAPIN IO> ...
3
votes
0answers
3k views

Firewalld - Logging denied packets enabled - not logging

I am using Firewalld and the drop zone is the default zone with an interface assigned to the zone. I then have rich rules to allow some traffic through the drop zone and I have enabled firewall-cmd -...
3
votes
0answers
1k views

Server went offline for no reason except SIGINT?

We had a system go offline this morning. The only thing in syslog is: Mar 20 15:27:15 fooserver systemd[1]: Received SIGINT. Mar 20 15:27:15 fooserver systemd[1]: Starting Synchronise Hardware Clock ...