Computing/Linux/RedHat

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Contents

General info

RHEL5

Notes

  • To perform a network install need to specify boot alternative at the initial installation screen
  • To restart GDM: killall gdm-binary

Yum

  • /etc/yum.conf - general config file
  • /etc/yum.repos.d - directory containing files with description of repositories (if not included into yum.conf directly)
  • /etc/yum -
  • useful commands:
    • yum install pkgname ... - install the latest version of a package
    • yum erase [pkgname ...] - remove specified packages
    • yum update [pkgname ...] - update all or specific packages
    • yum check-update - check if any updates are available
    • yum upgrade - to do OS version upgrades
    • yum search sometext - find packages matching the text string
    • yum deplist pkgname - list dependencies of a package
    • yum list all - list all available and installed packages
  • yum doesn't have the --force option available as up2date did. So, there are two ways to update kernel versions:
    • use yum to download the packages to local disk cache and then install them using rpm
    • comment out the appropriate exclusion line in /etc/yum.conf then run yum update
  • Repository priority policy
  • Files:
    • /etc/yum/yum.conf
    • /etc/yum/repos.d/
    • /etc/yum/pluginconf.d/
    • /var/cache/yum/

RHEL4

Notes

The ext2online utility has been added for online growing of existing ext3 file systems.
Note:
It is important to keep in mind that ext2online does not grow the underlying block device itself — there must be sufficient unused space already present on the device. The easiest way to ensure this is to use LVM volumes and to run lvresize or lvextend to extend the device.
In addition, file systems must be specially prepared in order to be resized past a certain point. The preparation involves reserving a small amount of space into which on-disk tables can grow. For newly-created file systems, mke2fs reserves such space automatically; the space reserved is sufficient to grow the file system by a factor of 1000. The creation of this reserved space can be disabled by the following command: mke2fs -O ^resize_inode
Future releases of Red Hat Enterprise Linux will allow the creation of this reserved space on existing file systems.
  • httpd
For example, a Boolean can be set to give specific permission to httpd to read objects in ~/public_html/ as long as they are labeled with the security context httpd_sys_content_t. The Apache daemon cannot access objects (files, applications, devices, and other processes) that have a security context not specifically granted access by SELinux to httpd.
Examples of relabeling include the following commands (one for recursively relabeling the contents of a directory, and one for relabeling a single file):
chcon -R -h -t httpd_sys_content_t public_html
chcon -t httpd_sys_content_t public_html/index.html
You can configure Boolean values or selectively disable targeted policy coverage for just Apache (or any of the covered daemons) using system-config-securitylevel.
  • PHP
The package now uses the "apache2handler" SAPI for integration with Apache httpd 2.0 rather than the "apache2filter" SAPI. If upgrading from previous releases, the SetOutputFilter directives should be removed from the /etc/httpd/conf.d/php.conf file.
  • X Windows
    At the present time, there are two font subsystems, each with different characteristics:
    • The original (15+ year old) subsystem is referred to as the "core X font subsystem". Fonts rendered by this subsystem are not anti-aliased, are handled by the X server, and have names like:
    -misc-fixed-medium-r-normal--10-100-75-75-c-60-iso8859-1
    • The newer font subsystem is known as "fontconfig", and allows applications direct access to the font files. Fontconfig is often used along with the "Xft" library, which allows applications to render fontconfig fonts to the screen with antialiasing. Fontconfig uses more human-friendly names like:
    Luxi Sans-10
    • Over time, fontconfig/Xft will replace the core X font subsystem. At the present time, applications using the Qt 3 or GTK 2 toolkits (which would include KDE and GNOME applications) use the fontconfig and Xft font subsystem; most everything else uses the core X fonts.
  • udev
    • Red Hat Enterprise Linux 4 has switched from a static /dev/ directory to one that is dynamically managed via udev. This allows device nodes to be created on demand as drivers are loaded.
    • Additional rules for udev should be placed in a separate file in the /etc/udev/rules.d/ directory.
    • Additional permission rules for udev should be placed in a separate file in the /etc/udev/permissions.d/ directory.

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