If I dual boot Ubuntu 20.04 with Ubuntu 20.04 will grub know how to handle it? I have a disk with a Ubuntu 20.04 partition and a 18.04 partition. If I update the 18.04 one to 20.04 I will have problems in grub?
Is it possible to dual boot two instances of Ubuntu 16.04? I've been programming for about a year and I'm very new to Ubuntu. I'm currently working on a project with a mentor who suggested partitioning part of my drive with a fresh Ubuntu install. I've never done anything like this and most of the guides I've seen are for dual-booting Ubuntu and Windows/MacOS.  I'm currently running Ubuntu 16.04 on my laptop. I was wondering If I could keep my current setup and also partition part of my drive with a fresh install of Ubuntu 16.04?
How to install mysql? Android: TextView automatically truncate and replace last 3 char of String How are parameters evaluated for a Plot in Manipulate I have an entry-level Nikon DSLR, and I cant decide if I should upgrade my camera body or upgrade from a  AF-S DX Nikkor 18-200mm to whatever else might be recommended? How do I change permissions on a FAT32 formatted drive? Every $k$ vertices in an $k$ - connected graph are contained in a cycle. Let $G$ be a $k$-connected graph. Meaning, $G$ has no fewer than $k$ vertices, and for every set of $k-1$ or fewer vertices, if we remove them from $G$, the graph stays connected (Of course, $G$ itself is also connected).  I want to prove that for any $k&gt;1$, if $G$ is $k$-connected, then every set of $k$ vertices is contained in a cycle.  I have tried some ways - mainly using induction by removing one of the vertices of the set from the graph, and/or using Menger's theorem to construct the cycle. But I always encounter problems with making sure that the cycle I'm building deosn't have repeating edges etc.  Help would be greatly appreciated :) Thanks! Tracking down where disk space has gone on Linux? When administering Linux systems I often find myself struggling to track down the culprit after a partition goes full. I normally use du / | sort -nr but on a large filesystem this takes a long time before any results are returned.  Also, this is usually successful in highlighting the worst offender but I've often found myself resorting to du without the sort in more subtle cases and then had to trawl through the output.  I'd prefer a command line solution which relies on standard Linux commands since I have to administer quite a few systems and installing new software is a hassle (especially when out of disk space!) In general what is the approach to switch the desktop environment or window manager on Ubuntu? The main difference between stock Ubuntu, Kubuntu and Lubuntu is supposedly the use of Unity vs. KDE vs. LXDE.  However, in order to try various desktop environments and window managers I don't want to have to reinstall the respective flavor from scratch just to get a particular desktop environments or window manager. There probably is an easier method than that.  The question: How can I easily test different desktop environments and respective compatible window managers (say KDE, LXDE, Unity, GNOME, XFCE and StumpWM)? What are Guinan's powers from Star Trek: TNG? In Star Trek: The Next Generation episode "" (Season 2, Episode 16) Q seems disturbed by the presence of Guinan to the point of raising his hands as if to use his powers on her. Guinan responds by raising her hands as if to cast a "magic" spell of her own.   Is it ever established what powers she or her race may possess? How does IPv4 Subnetting Work? This is a  about IPv4 Subnets.      Related:               How does Subnetting Work, and How do you do it by hand or in your head?  Can someone explain both conceptually and with several examples? Server Fault gets lots of subnetting homework questions, so we could use an answer to point them to on Server Fault itself.   If I have a network, how do I figure out how to split it up? If I am given a netmask, how do I know what the network Range is for it? Sometimes there is a slash followed by a number, what is that number? Sometimes there is a subnet mask, but also a wildcard mask, they seem like the same thing but they are different? Someone mentioned something about knowing binary for this? BBWC: in theory a good idea but has one ever saved your data? I'm familiar with what a BBWC (Battery-backed write cache) is intended to do - and previously used them in my servers even with good UPS. There are obvously failures it does not provide protection for. I'm curious to understand whether it actually offers any real benefit in practice.  (NB I'm specifically looking for responses from people who have BBWC and had crashes/failures and whether the BBWC helped recovery or not)  Update  After the feedback here, I'm increasingly skeptical as whether a BBWC adds any value.  To have any confidence about data integrity, the filesystem MUST know when data has been committed to non-volatile storage (not necessarily the disk - a point I'll come back to). It's worth noting that a lot of disks lie about when data has been committed to the disk (). While it seems reasonable to assume that disabling the on-disk cache might make the disks more honest, there's still no guarantee that this is the case either.  Due to the typcally large buffers in a BBWC, a barrier can require significantly more data to be commited to disk therefore causing delays on writes: the general advice is to disable barriers when using a non-volatile write back cache (and to disable on-disk caching). However this would appear to undermine the integrity of the write operation - just because more data is maintained in non-volatile storage does not mean that it will be more consistent. Indeed, arguably without demarcation between logical transactions there seems to be less opportunity to ensure consistency than otherwise.   If the BBWC were to acknowledge barriers at the point the data enters it's non-volatile storage (rather than being committed to disk) then it would appear to satisfy the data integrity requirement without a performance penalty - implying that barriers should still be enabled. However since these devices generally exhibit behaviour consistent with flushing the data to the physical device (significantly slower with barriers) and the widespread advice to disable barriers, they cannot therefore be behaving in this way. WHY NOT?  If the I/O in the OS is modelled as a series of streams then there is some scope to minimise the blocking effect of a write barrier when write caching is managed by the OS - since at this level only the logical transaction (a single stream) needs to be committed. On the other hand, a BBWC with no knowledge of which bits of data make up the transaction would have to commit its entire cache to disk. Whether the kernel/filesystems actually implement this in practice would require a lot more effort than I'm wiling to invest at the moment.  A combination of disks telling fibs about what has been committed and sudden loss of power undoubtedly leads to corruption - and with a Journalling or log structured filesystem which don't do a full fsck after an outage its unlikely that the corruption will be detected let alone an attempt made to repair it.   In terms of the modes of failure, in my experience most sudden power outages occur because of loss of mains power (easily mitigated with a UPS and managed shutdown). People pulling the wrong cable out of rack implies poor datacentre hygene (labelling and cable management). There are some types of sudden power loss event which are not prevented by a UPS - failure in the PSU or VRM a BBWC with barriers would provide data integrity in the event of a failure here, however how common are such events? Very rare judging by the lack of responses here.   Certainly moving the fault tolerance higher in the stack is significantly more expensive the a BBWC - however implementing a server as a cluster has lots of other benefits for performance and availability.  An alternative way to mitigate the impact of sudden power loss would be to implement a SAN - AoE makes this a practical proposition (I don't really see the point in iSCSI) but again there's a higher cost. Setting knots in natural cubic splines in R I have data with many correlated features, and I want to start by reducing the features with a smooth basis function, before running an LDA. I'm trying to use natural cubic splines in the splines package with the ns function.  How do I go about assigning the knots?  Here's the basic R code:  library(splines) lda.pred &lt;- lda(y ~ ns(x, knots=5))   But I have no idea about how to chose the knots in ns. Trouble downloading packages list due to a "Hash sum mismatch" error When I check for updates, I get a "Failed To Download Repository Information" error.   This is what comes up under details:   W: Failed to fetch gzip:/var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_natty_main_source_Sources  Hash Sum mismatch,  E: Some index files failed to download. They have been ignored, or old ones used instead. Problem with solving systems of linear congruence of two variables The problem I am given is finding a solution to the following pair of equations:  $3x + 4y$ $\equiv$ $5$ $mod$ $13$  $2x + 5y$ $\equiv$ $7$ $mod$ $13$  By reading the methodology here:   Since the modulos in my problem are also the same, I am able to use substitution, but this leaves fractions in my expressions.  I then used matrix multiplication as follows:  $\begin{bmatrix} 3 &amp; 4\\ 2 &amp; 5\end{bmatrix}$ $\begin{bmatrix}\ x\\ y\end{bmatrix}$ = $\begin{bmatrix}\ 5\\ 7\end{bmatrix}$   And solving this also gives me a matrix with fractions, so I am a bit lost on how to solve this problem.  Any help is appreciated. Thank you very much. What is an quick way to create a new blank file in Lion? In Windows, one can create a new file using Right Click -> Add New -> Type of File. Is there an analogous action in Lion?  I just want to create a new blank file on my Desktop. Prove $r^2+r_1^2+r_2^2+r_3^2=16R^2-a^2-b^2-c^2$ for a triangle with sides $a$, $b$, $c$, circumradius $R$, inradius $r$, exradii $r_1$, $r_2$, $r_3$ Padding is missing under the &quot;Communities&quot; border line, and the list is also showing &quot;Communities (0)&quot; (maybe the reason is due to caching as it shows 0 Communities):  Generally, padding is present: Until recently  had one single reputation point, you can see it in this old screenshot:    Now it has over 2K reputation all of a sudden.. what has caused this? Has it affected "real" members as well? What does 'exec {fd}</dev/watchdog' do in Bash That is literal, {fd} isn't a placeholder. I have a script that does this, and does not source in anything, nor does it reference {fd} anywhere else.  Is this valid bash?  exec {fd}&lt;/dev/watchdog How do I extract all the external links of a web page and save them to a file?