udev allows Linux users to have a dynamic /dev directory and it provides the ability to have persistent device names. In this tip you will learn about creating the static SCSI device name for /block/sdd as /dev/scsiharddisk.
A sudden outburst of violent disk I/O activity can bring down your email or web server. Usually, a web, mysql, or mail server serving millions and millions pages (requests) per months are prone to this kind of problem. Backup activity can increase current system load too. To avoid this kind of sudden outburst problem, run your script with scheduling class and priority. Linux comes with various utilities to manage this kind of madness.
Juliet Kemp shows you how to look after your bugs with Request Tracker, an enterprise-grade (and GPL’ed) ticketing system that can be used for project management, help desks, software development, and much more.
A TOP-like tool for monitoring system latency and its causes for Linux system.
The Intel Open Source Technology Center is pleased to announce the release of version 0.1 of LatencyTOP, a tool for developers to visualize system latencies. Skipping audio, slower servers, everyone knows the symptoms of latency. But to know what’s going on in the system, what’s causing the latency, how to fix it… that’s a hard question without good answers right now.
LatencyTOP is a Linux tool for software developers (both kernel and userspace), aimed at identifying where in the system latency is happening, and what kind of operation/action is causing the latency to happen so that the code can be changed to avoid the worst latency hiccups.
(Fig. 01: LatencyTOP in Action [ Image Credit: Intel Corp. ])
=> Visit official project site to download LatencyTOP software. Please note that you also need to patch Linux kernel.
rssh is a restricted shell for providing limited access to a host via ssh. It also allows system wide configuration and per user configuration. From the man page:
The user configuration directive allows for the configuration of options on a per-user basis. THIS KEYWORD OVERRIDES ALL OTHER KEYWORDS FOR THE SPECIFIED USER. That is, if you use a user keyword for user foo, then foo will use only the settings in that user line, and not any of the settings set with the keywords above. The user keywordâ€™s argument consists of a group of fields separated by a colon (:), as shown below. The fields are, in order:
- username : The username of the user for whom the entry provides options
- umask : The umask for this user, in octal, just as it would be specified to the shell access bits. Five binary digits, which indicate whether the user is allowed to use rsync, rdist, cvs, sftp, and scp, in that order. One means the command is allowed, zero means it is not.
- path : The directory to which this user should be chrooted (this is not a command, it is a directory name).
rssh examples of configuring per-user options
Open /etc/rssh.conf file:
# vi /etc/rssh.conf
All user tom to bypass our chroot jail:
Provide jerry cvs access with no chroot:
Provide spike rsync access with no chroot:
Provide tyke access with chroot jail located at /users
user="tyke:011:00001:/users" # whole user string can be quoted
if your chroot_path contains spaces, it must be quoted. Provide nibbles scp access with chroot directory:
user=nibbles:011:00001:"/usr/local/tv/shows/tom and jerry"
=> rssh home page
=> Redhat specific chroot jail script (outdated)
=> Refer man pages: rssh.conf, rssh, ssh, sshd, sftp, scp, rsync, sshd_config
Under Linux / UNIX you use lp command to print files from command prompt. lp is quite useful when GUI is not installed on Linux box to print files. The lp command is simply a front end command that calls the lpr command with appropriate options. Its main use is to allow the running of precompiled binary programs and scripts that assume that the lp command is the official printing command.
Changing papa size is very easy under GUI environment. But how do you change paper size under command prompt?
By default lp print to A4 paper size. However sometime you need to print to different paper size from command prompt such as A3 or A5. To print to A3 size, enter:
$ lp -o media=A3 /path/to/file
- -o media=size : Sets the page size to size. Most printers support at least the size names “a4”, “letter”, and “legal”.
Other useful examples
Print a double-sided legal document to a printer called “hpljf2”:
$ lp -d hpljf2 -o media=legal -o sides=two-sided-long-edge /path/to/file
Print an image across 4 pages using a printer called “epd2”:
$ lp -d epd2 -o scaling=200 filename
Print a text file with 12 characters per inch, 8 lines per inch, and a 1 inch left margin to a printer called “lpodc2”:
$ lp -d lpodc2 -o cpi=12 -o lpi=8 -o page-left=72 ~/info.txt
To know more about lp option, enter:
$ man lp
Please note that you need to configure print using CUPS configuration file /etc/cups/cupsd.conf or web based tool located at http://localhost:631/
(Fig 01: My CUPS Configuration, showing HP PhotoSmart Printer )