Linux

Tag: Linux

How To Clear Memory Cache In Linux (>= 2.6.16)

by Bryan on Dec.02, 2010, under Programming

Without getting into the politics of why you would want to clear your memory cache in Linux, here is a very small script I wrote to do just that. It makes use of a feature that was introduced in kernel 2.6.16, so your kernel version needs to be >= 2.6.16 in order to use this script. If you’re running a kernel older than that, you have bigger problems to worry about than your memory cache ;) If you don’t know how to determine your kernel version, you’re probably better off not messing with your memory cache.

free-cache:

#!/bin/bash
 
###
# This script flushes the file system buffers and clears memory caches.
# 
# From the man page:
#
# /proc/sys/vm/drop_caches (since Linux 2.6.16)
#
#   Writing to this file causes the kernel to drop clean caches, dentries and
#   inodes from memory, causing that memory to become free.
#
#   To free pagecache, use echo 1 > /proc/sys/vm/drop_caches
#   To free dentries and inodes, use echo 2 > /proc/sys/vm/drop_caches
#   To free pagecache, dentries and inodes, use echo 3 > /proc/sys/vm/drop_caches
#
# @Author Bryan C. Geraghty <bryan@ravensight.org>
# @Since 2010-11-01
##
 
sudo sync && sudo bash -c 'echo 3 > /proc/sys/vm/drop_caches';

1 Comment :Cache, Linux, Memory, Tips more...

Linux ACL Management Functions

by Bryan on Jan.07, 2010, under Programming, Security

Traditional file system permissions management in Linux leaves most users wanting. Fortunately, there’s a feature that most linux users don’t even know about called ACLs and it’s most likely already available on your system. All you have to do to enable it is add the `acl` option to your volume in `/etc/fstab` and re-mount the volume.

Once that is done, here are some functions that I wrote to help manage these ACLs.

Here is an example of a command that grants apache permission to read a directory with these functions:

$ source aclfunctions.bash; grantUserRead 'apache' /var/www '*';

aclfunctions.bash:

# Author :: Bryan Geraghty
# Date :: 2009-10-28
# Notes :: ACL management functions
 
##
# Resets permissions on all files and directories in the specified path and removes
# and ACL entries
#
# @param string $2 Base path Path in which all operations will take place
#
function resetAll
{
   echo "Resetting permissions on all files in directory $1";
 
   echo "Removing ACLs...";
   setfacl -Rb $1;
 
   echo "Resetting directories...";
   find $1 -type d -exec chmod 770 {} \;
 
   echo "Resetting files...";
   find $1 -type f -exec chmod 660 {} \;
}
 
## 
# Grants read permissions to all files/folders with names matching $3, which reside
# inside of directory $2, to user $1.
#
# @param string $1 Username The user to whom read permissions will be granted
# @param string $2 Base path Path in which all operations will take place
# @param string $3 Target Name of the file/directory on which to set the permissions
#
function grantUserRead
{
   echo "Granting read permission to user $1 on files/folders named $3 in directory $2";
 
   ## Set the default permissions for new files on the specified directory
   echo "Setting defaults...";
   find $2 -name "$3" -type d -exec setfacl -d -m u:$1:rx {} \;
 
   ## Recusively set the permissions on all existing directories and files within the
   ## specified directory
   echo "Setting directory permissions...";
   find $2 -name "$3" -type d -exec setfacl -R -m u:$1:rx {} \;
 
   ## Grant permissions to any files with the specified name
   echo "Setting file permissions...";
   find $2 -name "$3" -type f -exec setfacl -m u:$1:r {} \;
}
 
## 
# Grants write permissions to all files/folders with names matching $3, which reside
# inside of directory $2, to user $1.
#
# @param string $1 Username The user to whom read permissions will be granted
# @param string $2 Base path Path in which all operations will take place
# @param string $3 Target Name of the file/directory on which to set the permissions
#
function grantUserWrite
{
   echo "Granting write permission to user $1 on files/folders named $3 in directory $2";
 
   ## Set the default permissions for new files on the specified directory
   echo "Setting defaults...";
   find $2 -name "$3" -type d -exec setfacl -d -m u:$1:rwx {} \;
 
   ## Recusively set the permissions on all existing directories and files within the
   ## specified directory
   echo "Setting directory permissions...";
   find $2 -name "$3" -type d -exec setfacl -R -m u:$1:rwx {} \;
 
   ## Grant permissions to any files with the specified name
   echo "Setting file permissions...";
   find $2 -name "$3" -type f -exec setfacl -m u:$1:rw {} \;
}
 
## 
# Grants read permissions to all files/folders with names matching $3, which reside
# inside of directory $2, to group $1.
#
# @param string $1 Group The user to whom read permissions will be granted
# @param string $2 Base path Path in which all operations will take place
# @param string $3 Target Name of the file/directory on which to set the permissions
#
function grantGroupRead
{
   echo "Granting read permission to group $1 on files/folders named $3 in directory $2";
 
   ## Set the default permissions for new files on the specified directory
   echo "Setting defaults...";
   find $2 -name "$3" -type d -exec setfacl -d -m g:$1:rx {} \;
 
   ## Recusively set the permissions on all existing directories and files within the
   ## specified directory
   echo "Setting directory permissions...";
   find $2 -name "$3" -type d -exec setfacl -R -m g:$1:rx {} \;
 
   ## Grant permissions to any files with the specified name
   echo "Setting file permissions...";
   find $2  -name "$3" -type f -exec setfacl -m g:$1:r {} \;
}
 
## 
# Grants write permissions to all files/folders with names matching $3, which reside
# inside of directory $2, to group $1.
#
# @param string $1 Group The user to whom read permissions will be granted
# @param string $2 Base path Path in which all operations will take place
# @param string $3 Target Name of the file/directory on which to set the permissions
#
function grantGroupWrite 
{
   echo "Granting write permission to group $1 on files/folders named $3 in directory $2";
 
   ## Set the default permissions for new files on the specified directory
   echo "Setting defaults...";
   find $2 -name "$3" -type d -exec setfacl -d -m g:$1:rwx {} \;
 
   ## Recusively set the permissions on all existing directories and files within the
   ## specified directory
   echo "Setting directory permissions...";
   find $2 -name "$3" -type d -exec setfacl -R -m g:$1:rwx {} \;
 
   ## Grant permissions to any files with the specified name
   echo "Setting file permissions...";
   find $2 -name "$3" -type f -exec setfacl -m g:$1:rw {} \; 
}
 
## 
# Grants execute permissions to all files/folders with names matching $3, which reside
# inside of directory $2, to user $1.
#
# @param string $1 Username The user to whom read permissions will be granted
# @param string $2 Base path Path in which all operations will take place
# @param string $3 Target Name of the file/directory on which to set the permissions
#
function grantUserExec
{
   echo "Granting execute permission to user $1 on files/folders named $3 in directory $2";
 
   ## Set the default permissions for new files on the specified directory
   echo "Setting defaults...";
   find $2 -name "$3" -type d -exec setfacl -d -m u:$1:rwx {} \;
 
   ## Recusively set the permissions on all existing directories and files within the
   ## specified directory. One command will siffice for files and directories when
   ## setting execute permissions 
   echo "Setting directory and file permissions...";
   find $2 -name "$3" -exec setfacl -R -m u:$1:rwx {} \;
}
 
## 
# Grants execute permissions to all files/folders with names matching $3, which reside
# inside of directory $2, to group $1.
#
# @param string $1 Group The user to whom read permissions will be granted
# @param string $2 Base path Path in which all operations will take place
# @param string $3 Target Name of the file/directory on which to set the permissions
#
function grantGroupExec
{
   echo "Granting execute permission to group $1 on files/folders named $3 in directory $2";
 
   ## Set the default permissions for new files on the specified directory
   echo "Setting defaults...";
   find $2 -name "$3" -type d -exec setfacl -d -m g:$1:rwx {} \;
 
   ## Recusively set the permissions on all existing directories and files within the
   ## specified directory. One command will siffice for files and directories when
   ## setting execute permissions 
   echo "Setting directory and file permissions...";
   find $2 -name "$3" -exec setfacl -R -m g:$1:rwx {} \;
}