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

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113 views

How to troubleshoot rx_missed_errors?

Migrating from old server to new one, after setting all services, I notice a big dropped rx packets in my NIC: $ ifconfig eth2 | grep 'RX.*drop' RX packets:2059646370 errors:0 ...
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114 views

How to automate zabbix web scenarios for vhosts?

I'm new to Zabbix and enterprise monitoring. I've just finished installing Zabbix 2.4. I'm trying to monitor the state of all our vhosts dislocated on different servers. Until now the only solution ...
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656 views

Docker: Permission denied on folders added with ADD

I'm trying to configure a postgresql installation using docker. FROM ubuntu:13.10 ADD . /db # install postgres # ... RUN chown postgres:postgres /db -R && \ chmod 700 /db -R USER ...
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35 views

KVM host won't use memory for caching

I have a KVM host (Linux 3.14.32) running 8 virtual machines. They are overprovisioned (memory allocated for them is greater than available physical memory on the host). However they consume only ...
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255 views

Not Able to Mount USB HDD in Linux

I'm having a problem with a server that I just installed kernel 2.6.18-371.el5 on. It's an old kernel for Red Hat 5, I know, but due to certain "restrictions" I am forced into using that for the time ...
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58 views

How can I introspect the “shared subtree” mount flags for a particular mount?

Under Linux, the shared subtree flags control how a mountpoint is shared with parent and child mount namespaces. These flags include MS_SHARED, MS_PRIVATE, and MS_SLAVE. How can one see which of ...
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1k views

kworker consuming +90% IO and zero disk write

this is a standard apache web server on AWS Linux AMI + EBS. We are noticing high load average (+8) and iotop -a shows: Total DISK READ: 0.00 B/s | Total DISK WRITE: 2.37 M/s TID PRIO USER ...
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256 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 ...
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244 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 ...
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361 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 ...
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554 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 ...
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168 views

timing issue after route add/delete (route not used)

I have an application that is running a raw IP socket, destination of this socket is governed by routes installed via the 'ip route add' command. These routes can change during the lifetime of a ...
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137 views

grep is inconsistently defaulting to grep -P?

I have a script that does some housekeeping that works perfectly well when invoked from an interactive shell, but did nothing when invoked by cron. To troubleshoot this I started a shell with a ...
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315 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 ...
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0answers
99 views

reprepro use when multiple sources have the same codename

I'm investigating the use of reprepro to control what updates get propagated to our servers, and when. The idea is to vet updates by Debian and Ubuntu, and only apply the ones we choose. We want to ...
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2k 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 ...
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6k views

TCP Keepalive and firewall killing idle sessions

In a customer site, the network team added a firewall between the client and the server. This is causing idle connections to get disconnected after about 40 minutes of idle time. The network people ...
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823 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 ...
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1k 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 ...
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133 views

Linux device route without broadcast

I have the following setup: A network namespace, ns1 A pair of virtual interfaces, ns_ext1 and ns_int1. ns_ext exists in the global namespace, and ns_int1 exists in ns1. A GRE device, gre1, which ...
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0answers
50 views

How to apply memory limits to all cron jobs?

On a shared server (Debian Jessie), there are some memory limits (and other limits, like number of processes) that apply for a group of users, configured in /etc/security/limits.conf. It seems that ...
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24 views

Sparse files significantly larger (but still sparse) after copying over a network

When attempting to copy sparse VM image files from one KVM hypervisor to another over the network, I see the following behavior: The sparse files are still sparse files The copied sparse files are ...
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37 views

Q: MDADM mismatch_cnt > 0. Any way to identify which blocks are in disagreement?

Okay. After a routine scrub, my MDADM RAID5 is reporting mismatch_cnt = 16. As I understand, this means that while no device reported a read error, there are 16 blocks for which the data and parity ...
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29 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 ...
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43 views

What does the mkfs.ext4 -G option do?

On Microsoft's Best Practices for running Linux on Hyper-V page it is recommended to use ext4 and not ext3 and "specify the number of groups to be 4096" using mkfs.ext4 –G 4096 /dev/sdX1. What is this ...
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51 views

difference between ifdown, ifconfig stop and ONBOOT=no

my ifcfg-eth1 config as below DEVICE=eth1 TYPE=Ethernet UUID=5e4f36f8-14eb-4f0c-8fa9-3af9be3899a7 ONBOOT=no NM_CONTROLLED=yes BOOTPROTO=dhcp DEFROUTE=yes IPV4_FAILURE_FATAL=yes IPV6INIT=no ...
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147 views

Leap second addition in linux - how to make sure kernel detects it correctly

For the upcoming leap second addition on June 30 I have been working on making sure the Red Hat Linux detects the time smoothly. I have installed the updated tzdata and ntpd package on all RHEL5 and ...
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129 views

Data recovery for XFS partition

I want to recover data from a XFS partition. It seems that I need to xfs_repair the partition but I am not sure I would lose the data, so I prefer to ask to experts. I run a Virtual Box Linux Mint. ...
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94 views

How to find size of atomic write for nginx access log buffer?

This link says: The buffer size must not exceed the size of an atomic write to a disk file. For FreeBSD this size is unlimited. How can I find size of atomic write on my server? Is there any ...
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46 views

Can pacemaker retry monitor action on error?

I created simple pacemaker agent for managing MySQL. It works quite well, but there is 1 thing that I can't understand. When resource is "Started", and monitor action returns one of: ...
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55 views

Raid 1 seeding to speed up identical installs

I was thinking of installing Ubuntu on one of our Dell servers in a RAID 1 configuration, then using the mirrored drive as the primary drive in a second identical server with another RAID 1 setup. ...
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134 views

proc-sys-fs-binfmt_misc.automount failed service

I am using ubuntu 14.10. I have just installed systemd and I have a failing service, proc-sys-fs-binfmt_misc.automount. I've seen here it's a part of systemd: Is this file important? How do I solve ...
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184 views

elasticsearch fails periodically on ubuntu with systemd : how to resolve this?

I am using Elasticsearch on Ubuntu 14.10 and it's periodically going down (entering a failed state). When down, this throws exceptions on my website, users can't search, connect or update database ...
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0answers
67 views

Solving an asymetric HA Firewall/router

I have an old Linux HA firewall/router setup that never quite worked. As it was never quite put into true production (just testing and demo's), I always had to have one firewall shutdown to make it ...
3
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0answers
1k views

nginx recv() failed (104: Connection reset by peer) while reading response header from upstream

I have recently upgrade my magento from 1.5 to 1.9 and when ever I add a certain product to basket, I started to receive this error: 502 Bad Gateway There were no log entries in the var/log/ folder: ...
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583 views

Multiple Reverse SSH Tunnels using Single Port

I am able to accept reverse SSH connections from multiple remote systems on a single server using a port for each connection: Remote A: ssh -fN -R5000:localhost:22 user@server-ip -p22 Remote B: ssh ...
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36 views

Creating a linux-based black box environment?

This is a subject I've found very little on and while there are theory-based articles out there, I can't find anything with specifics. I also wasn't sure whether this should live on stack overflow or ...
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0answers
31 views

how do I plan partitions for LUKS encryption of a CentOS 7 server?

A CentOS 7 web server needs encryption at rest. I would like to use LUKS encryption for this, but I need direction to plan how. Can I use LUKS encryption to encrypt the entire drive as one unit on a ...
2
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0answers
16 views

Varnish failing intermittently for no obvious reason

For the last few years we have been running Varnish as a cache and load balancer in front of several apache servers serving several thousand websites. We also use monit to ensure that if varnish ...
2
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0answers
155 views

How to disable perf subsystem in Linux kernel?

I'm running some benchmarks. My benchmark runner monitors the dmesg buffer between experiments, looking for anything which could impact performance. Today it threw this up: [2015-08-17 10:20:14 ...
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0answers
97 views

Many gettimeofday in Apache 2.4 + fcgid + centos 6.6 - Long Wait time for static files

When i perform a strace on apache process, i see many gettimeofday before & after GET request, even when Apache returns a static file like an image file. It results in a long downtime period ...
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0answers
43 views

Get statuses of network printers

we are tasked with finding exactly how many pages were printed by all IP printers on a fairly large network, and then doing a lot of things with that data. There are about 15 different printer ...
2
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0answers
293 views

Problems on mounted NFS: 'No such file or directory' but files and directories exist

So we are having a medium-sized NFS4 storage server running CentOS 6.6 exporting an NFS share /storageDat (which is the NFS root, with two RAID volumes bound in there: ./dat1 and ./dat2); Export ...
2
votes
0answers
137 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 ...
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0answers
244 views

php generated css no output, net::ERR_INCOMPLETE_CHUNKED_ENCODING

I am running apache on an ubuntu installation. Several webapps are running on the same server. I installed a new app, which required the pdo-sqlite extension to be installed. Now my server is ...
2
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291 views

Not able to set memory limit on containers in docker

I am using ubuntu 14.04 with latest docker. No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 14.04.1 LTS Release: 14.04 3.18.5-x86_64-linode52 kernel But when i ...
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0answers
74 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 ...
2
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0answers
65 views

Move process across NUMA system

I am running many multi-threaded processes on a larger NUMA system with dozens of sockets. The memory access across different nodes is very slow, so I restrict each process to one socket and let it ...
2
votes
0answers
46 views

Dovecot and virtual domains with different namespaces

I've got dovecot 2.1.7 setup with virtual domains and now would like to have different public namespaces for each of the virtual domains. E.g. workdomain.com -> INBOX (private namespace) -> ...
2
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0answers
46 views

Tuning Amazon Linux worker tier

I have a worker tier that is using PHP process control (pcntl) functions to send multiple requests to the SNS service in parallel. My question is how best to tune MPM_PREFORK directives to get the ...