Posts Tagged ‘echo’
Friday, December 9th, 2011 I have few servers, which have automatically enabled IPv6 protocols (IPv6 gets automatically enabled on Debian), as well as on most latest Linux distribituions nowdays.
Disabling IPv6 network protocol on Linux if not used has 2 reasons:
1. Security (It’s well known security practice to disable anything not used on a server)
Besides that IPv6 has been known for few criticil security vulnerabilities, which has historically affected the Linux kernel.
2. Performance (Sometimes disabling IPv6 could have positive impact on IPv4 especially on heavy traffic network servers).
I’ve red people claiming disabling IPv6 improves the DNS performance, however since this is not rumors and did not check it personally I cannot positively confirm this.
Disabling IPv6 on all GNU / Linuces can be achieved by changing the kernel sysctl settings net.ipv6.conf.all.disable_ipv6 by default net.ipv6.conf.all.disable_ipv6 equals 1 which means IPv6 is enabled, hence to disable IPv6 I issued:
server:~# sysctl net.ipv6.conf.all.disable_ipv6=0
To set it permanently on system boot I put the setting also in /etc/sysctl.conf :
server:~# echo 'net.ipv6.conf.all.disable = 1 >> /etc/sysctl.conf
The aforedescribed methods should be working on most Linux kernels version > 2.6.27 in that number it should work 100% on recent versions of Fedora, CentOS, Debian and Ubuntu.
To disable IPv6 protocol on Debian Lenny its necessery to blackist the ipv6 module in /etc/modprobe.d/blacklist by issuing:
echo 'blacklist ipv6' >> /etc/modprobe.d/blacklist
On Fedora / CentOS there is a another universal “Redhat” way disable IPv6.
On them disabling IPv6 is done by editting /etc/sysconfig/network and adding:
NETWORKING_IPV6=no
IPV6INIT=no
I would be happy to hear how people achieved disabling the IPv6, since on earlier and (various by distro) Linuxes the way to disable the IPv6 is probably different.
Alto to stop Iptables IPV6 on CentOS / Fedora and RHEL issue:
# service ip6tables stop
# service ip6tables off
Tags: blackist, boot, Cannot, CentOS, conf, Debian, Disabling, distro, DNS, echo, fedora, gnu linux, heavy traffic, How to, impact, ipv, ipv4, ipv6, kernel, kernel 2, Linux, linux kernel, linux kernels, methodology, modprobe, Module, necessery, net, network, network protocol, network servers, Networking, number, performance, Protocol, protocols, quot, Redhat, security, security practice, security vulnerabilities, sysconfig, sysctl, system boot, traffic network, Ubuntu, version, way, working
Posted in Computer Security, Linux, System Administration, Various | No Comments »
Wednesday, September 16th, 2009 I tried using festival today just to realize it doesn’t work anymore.
For instance # echo test |festival -tts would fail with the annoying
“Linux: can’t open /dev/dsp” error message. I found the solution in ubuntuforums,
the solution is originally taken from “the Gentoo Speechd Howto“.
The solution is to create .festivalrc in your home as well as to the homes of all usersintending to use festival.
Here is how:
printf ";use ALSAn(Parameter.set 'Audio_Method 'Audio_Command)n(Parameter.set 'Audio_Command "aplay -q -c 1 -t raw -f s16 -r $SR $FILE")n" > .festivalrc
Tags: alsa, dev, doesn, dsp, echo, fix, home, Linux, message, solution, today, use, work
Posted in Linux and FreeBSD Desktop, Linux Audio & Video | No Comments »
Friday, February 14th, 2014 Lets say you're an admin involved in webhosting and due to a programmer's mistake, you end up with directory full with files with extension in upper cases but for actual version of website (all pictures are red only in lower cases), hence would like to transform these to lower cases.
To give an example, to illustrate what I mean, lets say you have in a directory files like;
filename.JPG, picture.PNG, new-picture.GIF
and you would like all files to be renamed to lower extension characters, i.e.:
filename.jpg, picture.png, new-picture.gif.
# find . -name '*.*' -exec sh -c 'a=$(echo {} | sed -r "s/([^.]*)\$/\L\1/"); [ "$a" != "{}" ] && mv "{}" "$a" ' \;
That's all enjoy 🙂
Tags: admin, directory, due, echo, end, JPG, Linux, Linux Rename, mistake, mv, picture, png, Rename
Posted in Linux, System Administration, Various | No Comments »
Monday, July 18th, 2011 Recently I had the task to add a range of few IP addresses to as a virtual interface IPs.
The normal way to do that is of course using the all well known ifconfig eth0:0, ifconfig eth0:1 or using a tiny shell script which does it and set it up to run through /etc/rc.local .
However the Redhat guys could omit all this mambo jambo and do it The Redhat way TM 😉 by using a standard method documented in CentOS and RHEL documentation.
Here is how:
# go to network-script directory[root@centos ~]# cd /etc/sysconfig/network-scripts
# create ifcfg-eth0-range (if virtual ips are to be assigned on eth0 lan interface[root@centos network-scripts]# touch ifcfg-eth0-range
Now inside ifcfg-eth0-range, open up with a text editor or use the echo command to put inside:
IPADDR_START=192.168.1.120
IPADDR_END=192.168.1.250
NETMASK=255.255.255.25
CLONENUM_START=0
Now save the /etc/sysconfig/network-scripts/ifcfg-eth0-range file and finally restart centos networking via the network script:
[root@centos network-scripts]# service network restart
That’s all now after the network gets reinitialized all the IPs starting with 192.168.1.120 and ending in 192.168.1.250< will get assigned as virtual IPs for eth0 interface
Cheers 😉
Tags: CentOS, CLONENUM, command, course, directory root, echo, echo command, eth, fedora linux, file, ifconfig eth0, ip addresses, ips, jambo, lan, lan interface, Linux, mambo jambo, Netmask, network, network scripts, Networking, range, rangeNow, Redhat, root, script directory, Shell, shell script, sysconfig, task, text, tiny shell, virtual interface, way
Posted in Linux and FreeBSD Desktop, System Administration | No Comments »
Saturday, July 9th, 2011 I’m currently writting a script which is supposed to be adding new crontab jobs and do a bunch of other mambo jambo.
By so far I’ve been aware of only one way to add a cronjob non-interactively like so:
linux:~# echo '*/5 * * * * /root/myscript.sh' | crontab -
Though using the | crontab – would work it has one major pitfall, I did completely forgot | crontab – OVERWRITES CURRENT CRONTAB! with the crontab passed by with the echo command.
One must be extremely careful if he decides to use the above example as you might loose your crontab definitions permanently!
Thanksfully it seems there is another way to add crontabs non interactively via a script, as I couldn’t find any good blog which explained something different from the classical example with pipe to crontab –, I dropped by in the good old irc.freenode.net to consult the bash gurus there 😉
So I entered irc and asked the question how can I add a crontab via bash shell script without overwritting my old existing crontab definitions less than a minute later one guy with a nickname geirha was kind enough to explain me how to get around the annoying overwridding.
The solution to the ovewrite was expected, first you use crontab to dump current crontab lines to a file and then you append the new cron job as a new record in the file and finally you ask the crontab program to read and insert the crontab definitions from the newly created files.
So here is the exact code one could run inside a script to include new crontab jobs, next to the already present ones:
linux:~# crontab -l > file; echo '*/5 * * * * /root/myscript.sh >/dev/null 2>&1' >> file; crontab file
The above definition as you could read would make the new record of */5 * * * * /root/myscript.sh >/dev/null be added next to the existing crontab scheduled jobs.
Now I’ll continue with my scripting, in the mean time I hope this will be of use to someone out there 😉
Tags: bash scripts, bash shell script, blog, classical example, cron, cron job, cron jobs, crontab, definitions, dev, echo, echo 5, echo command, exact code, file, fileThe, gurus, irc, jambo, kind, line, Linux, mambo jambo, mean time, minute, nbsp nbsp nbsp nbsp nbsp, nickname, ovewrite, pipe, pitfall, root, scripting, Shell, solution, someone, Thanksfully, time, use, way
Posted in Linux, System Administration | 9 Comments »
