Technical FAQ
From StackWiki
This is the StackWiki Technical Frequently Asked Questions (FAQ) page. This page is intended to provide short answers to common technical questions about technical aspects (such as Unix accounts and services). If more extensive information is available within the StackWiki, references to the relevant pages are given as well.
This page is open to edits by any Stack member. The Stack Helpdesk however maintains editorial control over the page.
Stack Accounts
Disk usage and quotas
How much disk space do I have available?
- Member accounts: Disk quotas are set on homedirectories (/home/username a.k.a. ~) and web space (/www/username a.k.a. ~/.html). A combined disk quotum is used, with a default value of 1.5 GB.
- Associational accounts: Separate quotas are set for the home directory space (/home/username a.k.a. ~) and web space (/www/username a.k.a. ~/.html). The current defaults are 10 GB for the home directory and 15 GB for web space.
Note that the values given above are defaults. Lower values do not occur, but it is possible to have higher diskquotas if more space is required (see below).
Data outside the home and web directories are not included in these numbers. E.g. mail boxes in /var/mail, SQL databases, Subversion repositories, anonymous FTP space, /slurp and /scratch etc. have no quota restrictions at all.
What are soft and hard quotas? What happens if I reach either value?
When we say you have a certain quota, we generally refer to the soft quota: the amount of space that you can freely use. However, when you reach this soft quota, nothing bad happens: writes to disk will still work for a bit, because we reserve a little additional space for everybody. Typically this is in the order of 10%. The hard quota is the absolute limit: if it is hit, any attempt to write more data into the quota-protected disk space will fail. Note that this extra space is not guaranteed in any way.
How can I check my disk space usage and quota status?
When logged in on a Stack login server (for associational accounts: vwww/www.stud.tue.nl), you can issue the shell commandshowquota -v. This command will output both the disk quota and the current disk usage.
I'd like a larger disk quota. Is this possible, and if so, how?
It is generally possible to have your disk quotas extended. To apply for this quota extension, please send a mail to the Unix Committee including a reason for extension and an indication of how much space is needed. Be reasonable in your request.
Please note that having a larger quota does not imply that you can waste gigabytes of space. Your Stack home directory space is not meant to back up your computer at home, or leave around a bunch of ISO images. Stack can and will not provide lots of space for such purposes in home directories. Stack utilizes a high-end enterprise level, fast, very reliable but expensive storage and backup system so waste should be avoided.
Why does Stack use quotas, when they can be easily extended when more space is needed?
Even with users' best intensions, it occasionally happens a process goes crazy and starts filling up the disk with large files (e.g. coredumps). Without per-user restrictions, a problem with a single user account would quickly fill up the disk, creating a problem for many or all users. Implementing user quota avoids this.
A second reason is that space is less easily wasted when the available space is limited. More space may be awarded easily, but by having to request it, the user takes responsibility, indicating the current space is not being wasted yet needs to be extended for legitimate use.
Uhm, quotum, quota, or quotas?
Technically, a single limit would be a 'quotum', and the plural is 'quota'. However, in common speech, 'quota' is oft used for the singular and 'quotas' as the plural. We could be pedantic about it, but it's not worth it; it should be obvious from the context what is meant.
Stack network
External connectivity
How is Stack connected to the outside world (the internet)?
The Stack network is a part of the network of the TUE. Stack is connected to the university network (in De Hal) using two gigabit copper (1000baseT) connections. The second gigabit connection is inactive under normal conditions; it serves to provide a redundant path in case the first path fails due to a component failure. These two gigabit connections are with two different university switches, which in turn are connected to the university backbone (and ultimately the internet) using 10Gbit ethernet.
Stack currently has two machines outside De Hal. First, there is one SGI Origin 2000 (copenhagen) in the Laplace building, connected using 100Mbit. More importantly, one server is located outside the university, at Dispuut Interlink at Fontys Hogescholen Eindhoven. This server, weber, runs the status.stack.nl website that informs users about network or systems maintenance and problems.
Can I ping the network from outside the TUE network?
The university firewall prevents ICMP echo requests, or "pings" from the outside world. So pinging Stack servers from outside the TUE network won't work. However, if you really want to query the Stack network using ICMP echo requests, you can ping the system stack-gw.stack.nl from anywhere. This system is accessible by 'ping' from anywhere. Trying another host or IP address is not guaranteed to work.
Wireless networking
Is wireless networking available at Stack?
Yes. Wireless "WiFi" 802.11 networking is avaiable at Stack as well as outside the Stack room (both Stekkercafe and outside the building). Network connectivity is offered both by the university (SSIDs are TUE, TUE-WPA2, Eduroam and guest) and Stack (SSID STACK), both with radio's supporting 802.11b/g (up to 54Mbps). Stack recommends the use of Stack's own wireless network instead of the university network.
How can I connect to the Stack wireless network?
Note: this section describes a network configuration which is currently being deployed. Details may be out of date.
- STACK: The Stack wireless network can be used by all Stack members as well as guests. To use the STACK network, registration of the MAC address of the device is required. Currently these registrations can only be performed by the Unix Committee but this will be extended such that members can register their own MAC addresses. Network security is implemented using WPA-TKIP ("plain WPA"). Guests of Stack can apply to members of the board or the Unix Committee for registration. A sample configuration for wpa_supplicant on Unix systems (obtain the current key from sysadmins at Stack):
network={
ssid="stack"
psk="geheim"
}
- IE2: This is the previous generation of Stack wireless network. It is currently being phased out and does not accept new registrations. Access is also based on MAC address; the network is secured using WEP-PSK.
How can I connect to the wireless university networks offered by the university?
- TUE: This is the network for university students and employees. It requires a university NT account to connect as well as registration of the MAC address. Students can request either at the Notebook Service Centrum (NSC), conveniently located directly opposite Stack at the other end of the Stekkercafe. The TUE network is secured using dynamic WEP keys exchanged using the PEAP protocol. A manual can be found on the NSC website.
- TUE-WPA2: This network has the same requirements and purposes as the TUE network. It does however use WPA2 for increased security. More documentation can be found on the Brewery, the TU/e Dienst ICT Documentation site. Note that this site is only available from within the university network. A sample configuration for wpa_supplicant on Unix systems:
network={
ssid="tue-wpa2"
key_mgmt=WPA-EAP
eap=PEAP
identity="s123456"
password="geheim"
}
Note for Ubuntu users: Due to a bug in the network manager in (K/X)Ubuntu 8.10, computers running this OS cannot authenticate with TU/e wireless. An easy workaround is installing wicd. Installing wicd will uninstall network-manager. After a reboot, you will see wicd icon instead of classic network manager. There you can choose "tue-wpa2" network, click "Advanced Settings", choose "PEAP with GTC" as the encryption and input s-number and password. Also checking the box "Use these settings for all networks sharing this essid" will help automatically connecting.
- Eduroam: The purpose of the Eduroam network is to let students (and possibly employees) from different universities to connect to wireless networks at other universities. For more information, see the national Eduroam website. Connecting to the Eduroam network will permit internet access, but is not part of the university's internal network.
- guest: This is a network allowing registered guests of the university to have internet access. Like eduroam, it does not provide access to the internal university network. Note that while the guest network seems open, the internet is not accessible without a registration. These registrations are given out on an individual basis by the university departments.
Some more references to guides for setting up the various wireless networks using e.g. Linux with nm-applet or Macs may be found in the Helpdesk documentation section.
