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%\usepackage{opensans}          % Can't make this work so far. Shame. Would be lovely.
\usepackage[normalem]{ulem}     % For underlining links
% Most of the following are not required for the majority
% of cheat sheets but are needed for some symbol support.
\usepackage{amsmath}            % Symbols
\usepackage{MnSymbol}           % Symbols
\usepackage{wasysym}            % Symbols
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% Document Info
\author{rpolyano}
\pdfinfo{
  /Title (operating-system-basics.pdf)
  /Creator (Cheatography)
  /Author (rpolyano)
  /Subject (Operating System Basics Cheat Sheet)
}

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% Header and Footer
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\fancyhead[L]{
\noindent
\begin{multicols}{3}
\begin{tabulary}{5.8cm}{C}
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    \vspace{-7pt}
    {\parbox{\dimexpr\textwidth-2\fboxsep\relax}{\noindent
        \hspace*{-6pt}\includegraphics[width=5.8cm]{/web/www.cheatography.com/public/images/cheatography_logo.pdf}}
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\columnbreak
\begin{tabulary}{11cm}{L}
    \vspace{-2pt}\large{\bf{\textcolor{DarkBackground}{\textrm{Operating System Basics Cheat Sheet}}}} \\
    \normalsize{by \textcolor{DarkBackground}{rpolyano} via \textcolor{DarkBackground}{\uline{cheatography.com/24960/cs/6373/}}}
\end{tabulary}
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\fancyfoot[L]{ \footnotesize
\noindent
\begin{multicols}{3}
\begin{tabulary}{5.8cm}{LL}
  \SetRowColor{FootBackground}
  \mymulticolumn{2}{p{5.377cm}}{\bf\textcolor{white}{Cheatographer}}  \\
  \vspace{-2pt}rpolyano \\
  \uline{cheatography.com/rpolyano} \\
  \end{tabulary}
\vfill
\columnbreak
\begin{tabulary}{5.8cm}{L}
  \SetRowColor{FootBackground}
  \mymulticolumn{1}{p{5.377cm}}{\bf\textcolor{white}{Cheat Sheet}}  \\
   \vspace{-2pt}Not Yet Published.\\
   Updated 13th May, 2016.\\
   Page {\thepage} of \pageref{LastPage}.
\end{tabulary}
\vfill
\columnbreak
\begin{tabulary}{5.8cm}{L}
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  \mymulticolumn{1}{p{5.377cm}}{\bf\textcolor{white}{Sponsor}}  \\
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  \vspace{-5pt}
  %\includegraphics[width=48px,height=48px]{dave.jpeg}
  Measure your website readability!\\
  www.readability-score.com
\end{tabulary}
\end{multicols}}




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% Set font size to small. Switch to any value
% from this page to resize cheat sheet text:
% www.emerson.emory.edu/services/latex/latex_169.html
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\begin{multicols*}{3}

\begin{tabularx}{5.377cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Address Translation}}  \tn
% Row 0
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{VA -\textgreater{} Page Table (entry) -\textgreater{} Physical memory or swap} \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
\mymulticolumn{1}{x{5.377cm}}{Temporal Locality - recently referenced pages that might be again} \tn 
% Row Count 4 (+ 2)
% Row 2
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{Spatial Locality - referenced addresses will probably be near other recently referenced} \tn 
% Row Count 6 (+ 2)
% Row 3
\SetRowColor{white}
\mymulticolumn{1}{x{5.377cm}}{Mappings cached in TLB (Translation Lookaside Buffer)} \tn 
% Row Count 8 (+ 2)
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{5.377cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Page Tables}}  \tn
% Row 0
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{Entry looks like `| M\textasciicircum{}1\textasciicircum{} | R\textasciicircum{}1\textasciicircum{} | V\textasciicircum{}1\textasciicircum{} | Prot\textasciicircum{}3\textasciicircum{} |    PFN\textasciicircum{}26\textasciicircum{}    |`} \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
\mymulticolumn{1}{x{5.377cm}}{{\bf{M}}odify Bit - whether or not a page has been written (set on write)} \tn 
% Row Count 4 (+ 2)
% Row 2
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{{\bf{R}}eference Bit - page has been accessed (set on read/write)} \tn 
% Row Count 6 (+ 2)
% Row 3
\SetRowColor{white}
\mymulticolumn{1}{x{5.377cm}}{{\bf{V}}alid bit - PTE can be used} \tn 
% Row Count 7 (+ 1)
% Row 4
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{{\bf{Prot}}ection bits - R/W/X permissions} \tn 
% Row Count 8 (+ 1)
% Row 5
\SetRowColor{white}
\mymulticolumn{1}{x{5.377cm}}{{\bf{PFN}} - Page Frame Number - physical page} \tn 
% Row Count 9 (+ 1)
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{5.377cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Other Page Tables}}  \tn
% Row 0
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{Hashed - Hash function maps virtual page to bucket of LList of (VPN, PTE)} \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
\mymulticolumn{1}{x{5.377cm}}{Inverted - Table of PFNs - \textgreater{} PID, PTE} \tn 
% Row Count 3 (+ 1)
\hhline{>{\arrayrulecolor{DarkBackground}}-}
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\par\addvspace{1.3em}

\begin{tabularx}{5.377cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Fetch Policies}}  \tn
% Row 0
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{{\bf{Demand Paging}} - Swap in the pages you need when you need them} \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
\mymulticolumn{1}{x{5.377cm}}{{\bf{Prepaging}} - Predict next page that will get loaded and load it now} \tn 
% Row Count 4 (+ 2)
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{5.377cm}{p{0.54747 cm} x{4.42953 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{5.377cm}}{\bf\textcolor{white}{Replacement Policies}}  \tn
% Row 0
\SetRowColor{LightBackground}
OPT & Swap out page that will not be used for the longest time \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
FIFO & Swap out oldest page \tn 
% Row Count 3 (+ 1)
% Row 2
\SetRowColor{LightBackground}
 & Suffers Belady's Anomaly - Fault rate {\bf{may}} increase with memory size \tn 
% Row Count 6 (+ 3)
% Row 3
\SetRowColor{white}
LRU & Swap out page that has not been accessed for longest time \tn 
% Row Count 8 (+ 2)
% Row 4
\SetRowColor{LightBackground}
CLOCK & Approximation of LRU - Go through candidates in a circle. If Ref bit set, clear it, move on. If not set, then swap out. \tn 
% Row Count 12 (+ 4)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\SetRowColor{LightBackground}
\mymulticolumn{2}{x{5.377cm}}{{\bf{Page Buffering}} - Maintain a pool of free (uncleared/rescuable) frames. Run replacement when pools gets too empty, run it until pull is full enough. On fault grab frame from pool.}  \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}--}
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\begin{tabularx}{5.377cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Address Space}}  \tn
\SetRowColor{LightBackground}
\mymulticolumn{1}{p{5.377cm}}{\vspace{1px}\centerline{\includegraphics[width=5.1cm]{/web/www.cheatography.com/public/uploads/rpolyano_1449866286_asd.PNG}}} \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}-}
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\begin{tabularx}{5.377cm}{x{1.29402 cm} x{3.68298 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{5.377cm}}{\bf\textcolor{white}{Deadlock}}  \tn
% Row 0
\SetRowColor{LightBackground}
{\bf{Definition}} & Set of processes that compete for resources or communicate with each other permanently blocked \tn 
% Row Count 4 (+ 4)
% Row 1
\SetRowColor{white}
{\bf{Conditions}} & Mutual Exclusion* - only one process uses resource at once \tn 
% Row Count 6 (+ 2)
% Row 2
\SetRowColor{LightBackground}
 & Hold and wait* - A process may hold resource while waiting for other resource \tn 
% Row Count 9 (+ 3)
% Row 3
\SetRowColor{white}
 & No preemption* - No resource can be forcefully removed from a process \tn 
% Row Count 12 (+ 3)
% Row 4
\SetRowColor{LightBackground}
 & Circular wait** - A closed chain of processes, where one needs 1+ resources held by the next. \tn 
% Row Count 16 (+ 4)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\SetRowColor{LightBackground}
\mymulticolumn{2}{x{5.377cm}}{{\emph{Necessary for deadlock.  \newline }}* Necessary and sufficient.}  \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}--}
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\begin{tabularx}{5.377cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Memory partitioning (Fixed vs Dynamic)}}  \tn
% Row 0
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{- {\bf{{\emph{Fixed partitioning:}}}} Every process gets a fixed amount of memory in one of the following ways:} \tn 
% Row Count 3 (+ 3)
% Row 1
\SetRowColor{white}
\mymulticolumn{1}{x{5.377cm}}{- {\bf{Equal size.}} Every process gets the same amount of memory. Internal fragmentation when process too small. Overlay when process too big. No external fragmentation.} \tn 
% Row Count 7 (+ 4)
% Row 2
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{- {\bf{Unequal size.}} Every process gets a chunk that has minimum memory required available. Internal fragmentation. Holes} \tn 
% Row Count 10 (+ 3)
% Row 3
\SetRowColor{white}
\mymulticolumn{1}{x{5.377cm}}{- {\bf{{\emph{Dynamic partitioning:}}}} Size and number of partitions varies} \tn 
% Row Count 12 (+ 2)
% Row 4
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{- {\bf{Every process}} gets as much as needed on start. Need to know size beforehand. Holes. Need relocatable processes.} \tn 
% Row Count 15 (+ 3)
% Row 5
\SetRowColor{white}
\mymulticolumn{1}{x{5.377cm}}{- {\bf{{\emph{PAGING}}}}: Split both virtual and physical memory in same chunks called {\bf{Pages}}} \tn 
% Row Count 17 (+ 2)
% Row 6
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{- Every process gets its own {\bf{Page Table}} which maps its virtual addresses into physical pages (offset is the same, only need to translate frames)} \tn 
% Row Count 20 (+ 3)
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{5.377cm}{x{1.84149 cm} x{3.13551 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{5.377cm}}{\bf\textcolor{white}{CPU Scheduling}}  \tn
% Row 0
\SetRowColor{LightBackground}
{\bf{FCFS}} & NP, First Come First Serve \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
{\bf{SJF}} & NP or P, Choose thread with shortest (remaining) processing time. Optimal avg wait time \tn 
% Row Count 6 (+ 4)
% Row 2
\SetRowColor{LightBackground}
{\bf{RR}} & P, Circular Q, good for time sharing systems \tn 
% Row Count 8 (+ 2)
% Row 3
\SetRowColor{white}
{\bf{Priority Scheduling}} & NP or P, Highest priority job selected from ready Q \tn 
% Row Count 11 (+ 3)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\SetRowColor{LightBackground}
\mymulticolumn{2}{x{5.377cm}}{NP - Nor Preemptive Preemptive  \newline Priority Inversion - Low priority blocks resource, high priority doesn't run.}  \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{5.377cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Log FS Mapping and GC}}  \tn
\SetRowColor{white}
\mymulticolumn{1}{x{5.377cm}}{{\bf{Mappings}} to inodes are stored in imaps, placed in chunks after new information. Fixed location on disk called Checkpoint Region contains pointers to latest pieces of imap. Keep 2 CRs at opposite ends of the disk for redundancy. \newline % Row Count 5 (+ 5)
{\bf{Garbage Collection}} periodically goes through segment by segment and frees up files, since new versions of files are written to new places on disk. (LOG FS is circular)% Row Count 9 (+ 4)
} \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{5.377cm}{x{0.84609 cm} x{4.13091 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{5.377cm}}{\bf\textcolor{white}{Disk Performance}}  \tn
% Row 0
\SetRowColor{LightBackground}
Seek & Moving disk arm to cylinder (1 - 15ms, \textasciitilde{}5ms avg, improving slowly) \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
\seqsplit{Rotation} & Wait for sector to rotate to head (4ms avg, not improving) \tn 
% Row Count 4 (+ 2)
% Row 2
\SetRowColor{LightBackground}
\seqsplit{Transfer} & Moving data from platter to controller (\textasciitilde{}100MB/s, sector \textasciitilde{}5microseconds, Improving quickly) \tn 
% Row Count 7 (+ 3)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{5.377cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{FS - Caching Writes}}  \tn
% Row 0
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{Writes can be buffered. This allows} \tn 
% Row Count 1 (+ 1)
% Row 1
\SetRowColor{white}
\mymulticolumn{1}{x{5.377cm}}{Multiple writes in one (e.x. flip many bits of a bitmap)} \tn 
% Row Count 3 (+ 2)
% Row 2
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{Scheduling to allow for better disk access} \tn 
% Row Count 4 (+ 1)
% Row 3
\SetRowColor{white}
\mymulticolumn{1}{x{5.377cm}}{Avoid writes entirely (e.x. set bit to 1, set bit to 0)} \tn 
% Row Count 6 (+ 2)
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{5.377cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{File Buffer Cache}}  \tn
% Row 0
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{Locality when reading/writing files} \tn 
% Row Count 1 (+ 1)
% Row 1
\SetRowColor{white}
\mymulticolumn{1}{x{5.377cm}}{Cache blocks/inodes/dir entries that are "hot"} \tn 
% Row Count 2 (+ 1)
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{Can use static or dynamic partitioning. \newline {\bf{Static}} - allocate n\% at boot. Wasteful. \newline {\bf{Dynamic}} - VM and FS pages into unified cache. Pages of memory can be dynamically allocated between RAM and FS cache}  \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{5.377cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Fast File System}}  \tn
% Row 0
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{Used cylinder (block) groups.} \tn 
% Row Count 1 (+ 1)
% Row 1
\SetRowColor{white}
\mymulticolumn{1}{x{5.377cm}}{Data blocks in same file allocated in same group} \tn 
% Row Count 2 (+ 1)
% Row 2
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{Entries in same directory allocated in same group} \tn 
% Row Count 3 (+ 1)
% Row 3
\SetRowColor{white}
\mymulticolumn{1}{x{5.377cm}}{Inodes for files are allocated in same group as file data} \tn 
% Row Count 5 (+ 2)
% Row 4
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{Large files get broken up into chunks and allocated in different cylinder groups} \tn 
% Row Count 7 (+ 2)
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{Groups reduce number of long seeks. \newline Must have free space in cylinder groups (10\% of disk reserved free)}  \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{5.377cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Disk Scheduling Policies}}  \tn
% Row 0
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{{\bf{FCFS}} - First Come First Serve (i.e. no scheduling) - Good under small load} \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
\mymulticolumn{1}{x{5.377cm}}{{\bf{SSTF}} (Shortest Seek Time First) - Minimize arm movement, maximize request rate, favor middle blocks} \tn 
% Row Count 5 (+ 3)
% Row 2
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{{\bf{SCAN}} (elevator) - Order requests by direction (do all in direction one, then all in reverse)} \tn 
% Row Count 7 (+ 2)
% Row 3
\SetRowColor{white}
\mymulticolumn{1}{x{5.377cm}}{{\bf{C-SCAN}} (Typewriter) - Like SCAN, but only in one direction.} \tn 
% Row Count 9 (+ 2)
% Row 4
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{{\bf{LOOK/C-LOOK}} - Same as SCAN/C-SCAN but only move as far as last request in each direction.} \tn 
% Row Count 11 (+ 2)
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{5.377cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Journaling}}  \tn
% Row 0
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{Log TxBegin , log inode bitmap, log block bitmap, log block data. Once done, log txend (transaction committed)} \tn 
% Row Count 3 (+ 3)
% Row 1
\SetRowColor{white}
\mymulticolumn{1}{x{5.377cm}}{Write data (checkpoint step). Make sure TxEnd scheduled last.} \tn 
% Row Count 5 (+ 2)
% Row 2
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{Avoid writing data to journal by writing data first, then journal, then actual metadata} \tn 
% Row Count 7 (+ 2)
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{5.377cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Log FS}}  \tn
% Row 0
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{Like FFS but everything gets logged in order.} \tn 
% Row Count 1 (+ 1)
% Row 1
\SetRowColor{white}
\mymulticolumn{1}{x{5.377cm}}{Superblock | summary | inode | data | data | inode | data | superblock | summary etc} \tn 
% Row Count 3 (+ 2)
% Row 2
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{Summary has pointer to next summary or next super block.} \tn 
% Row Count 5 (+ 2)
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{5.377cm}{x{1.89126 cm} x{3.08574 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{5.377cm}}{\bf\textcolor{white}{RAID (Redundant Array of Independent Disks}}  \tn
% Row 0
\SetRowColor{LightBackground}
RAID1 (Data duplication) & mirror images, redundant full copy. Wastes space \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
Parity Information & XOR each bit from2 drives, store checksum on 3rd \tn 
% Row Count 4 (+ 2)
% Row 2
\SetRowColor{LightBackground}
RAID 0 & Write half of data on one drive and one on the other \tn 
% Row Count 7 (+ 3)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{5.377cm}{x{1.44333 cm} x{3.53367 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{5.377cm}}{\bf\textcolor{white}{Filesystem consistency}}  \tn
% Row 0
\SetRowColor{LightBackground}
Superblock & Sanity checks. Use another copy if corrupted \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
Free blocks & Ensure inodes in use are marked in bitmap. Trust inodes. \tn 
% Row Count 4 (+ 2)
% Row 2
\SetRowColor{LightBackground}
Inode state & Must have valid mode. Remove if can't fix \tn 
% Row Count 6 (+ 2)
% Row 3
\SetRowColor{white}
Inode links & Verify links. Traverse tree and count links. Move unlinked inodes to lost+found \tn 
% Row Count 9 (+ 3)
% Row 4
\SetRowColor{LightBackground}
Duplicates & Two inodes refer to same block \tn 
% Row Count 11 (+ 2)
% Row 5
\SetRowColor{white}
Bad blocks & bad pointers. Remove from inode \tn 
% Row Count 13 (+ 2)
% Row 6
\SetRowColor{LightBackground}
Directory checks & Make sure . and .. are first. Each inode in dir is allocated. No dir linked more than once. \tn 
% Row Count 17 (+ 4)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{5.377cm}{x{1.54287 cm} x{3.43413 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{5.377cm}}{\bf\textcolor{white}{CPU Scheduling Goals}}  \tn
% Row 0
\SetRowColor{LightBackground}
All Systems & Fairness, Avoid starvation, Policy enforcement, Best use of resources \tn 
% Row Count 3 (+ 3)
% Row 1
\SetRowColor{white}
Batch System & Throughput (jobs/hour), Turnaround (min time between submit and complete), CPU Util (keep CPU busy) \tn 
% Row Count 7 (+ 4)
% Row 2
\SetRowColor{LightBackground}
Interactive System & Response time (min time from submit to start), Proportionality (simple tasks finish faster) \tn 
% Row Count 11 (+ 4)
% Row 3
\SetRowColor{white}
Real Time System & Meet deadlines, predictability \tn 
% Row Count 13 (+ 2)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{5.377cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Threads}}  \tn
% Row 0
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{{\bf{Kernel}} - Less state to alloc and init than process =\textgreater{} cheaper concurrency} \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
\mymulticolumn{1}{x{5.377cm}}{{\bf{User}} - Managed by runtime systems. Small, fast, has PC, registers, stack, small TCB. Creating, switching, sync done by procedures (no kernel). (Disadv.) - Not well integrated with OS, Scheduling.} \tn 
% Row Count 6 (+ 4)
% Row 2
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{{\bf{Hybrid}} - Can have many kernel threads associated with many user threads, or many user threads associated with a few kernel threads.} \tn 
% Row Count 9 (+ 3)
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\end{tabularx}
\par\addvspace{1.3em}


% That's all folks
\end{multicols*}

\end{document}