System information

3 Software of the CHARM
utilities. It replaces the most of the utilities usually found in GNU
3
fileutils, shellutils, etc.
However, the utilities in BusyBox generally have fewer options than their full-featured GNU
counterparts. Third party software like ssh or the web server axhttpd are located in the
directory /usr/local/bin or /usr/local/sbin. By the reason of the limitation of write cycles to
the flash unit the permanently altered files like log files and temporary application data are
stored in a temporary file storage (tmpfs) facility using virtual memory [53]. The directory
/ext (extension) is mounted on the last MTD partition. It contains the CHARM specific
software like USB Firmware, VNC server and VGA BIOS content. But the CHARM related
drivers are the sole exception and are stored in /lib/modules on the third MTD partition.
Table 3.3 depicts the directory structure of the root file system of the CHARM.
Location Directory Applications
MTD 3 /bin/ BusyBox
/sbin/ BusyBox
/etc/ Standard configuration files and boot scripts.
/lib/ Libraries and modules.
/usr/www/ Web pages.
/usr/share/udhcpc/ Script for the DHCP client.
/usr/lib/ Contains sendmail.
/usr/local/bin/ Third party programs.
tmpfs /var/ Log files and application storage
/tmp/ Directory for temporary content storage.
MTD 4 /ext/bin/ CHARM specific programs
/ext/etc/ CHARM specific configuration files and boot scripts.
/ext/usr/share/ USB Firmware, VGA BIOS ROM and other applica-
tion data.
/ext/lib/ JPEG Library (used by the VNC server)
Table 3.3: Directory structure of the Root File System
3.4 NFS-Directory
The amount of software stored on the CHARM is limited to the size of the flash memory.
To obtain additional storage capabilities, the CHARMs connects to a central NFS
4
server
in an automatic way. After receiving the initial DHCP
5
response, the cards mount the NFS
share. Picture 3.2 illustrates this process. The DHCP response contains the host name of
the NFS server and the directory name of the NFS share. If the DHCP server does not
provide information about the NFS server, the CHARM uses the default settings to mount
the NFS directory. Table 3.4 lists the default settings of the NFS connection defined for
the CHARM.
3
GNU is a recursive acronym that stands for "GNU’s Not Unix".
4
Network File System [54].
5
Dynamic Host Configuration Protocol [55].
38