Linux and Git Field Notes

A collection of Linux and Git commands from my notes. Rough around the edges — preserved as written.

---

PDF, Packages, Dropbox, and Process Management

Split pages from a PDF (requires pdftk):

pdftk old.pdf cat 1-9 26-end output new.pdf

Export list of manually installed packages:

aptitude search '!~M ~i' | awk -F " " '{ print "apt-get -y install " $2 }' > aptshell.sh

Start Dropbox daemon:

~/.dropbox-dist/dropboxd

Useful ps commands:

ps aux                  # all running processes
ps -A                   # every process on the system
ps -U root -u root -N   # every process except root
ps -u vivek             # processes for a specific user
top                     # dynamic real-time view
pstree                  # tree view of processes

Check disk usage by depth:

du --max-depth=1   # first tier only
du --max-depth=0   # same as -s, just the total

Download files with wget:

wget <url>
wget <url> -t 5    # retry up to 5 times (useful for broken downloads)

---

Create ISO Files from the Terminal

From a folder:

mkisofs -r -o /isofile.iso /folder

From specific files:

mkisofs -r -o /isofile.iso /mybigfile
mkisofs -r -o /isofile.iso *.mp3

From a CD/DVD drive:

dd if=/dev/cdrom0 of=isofile.iso

---

GCC: Preprocessed Output, Object Code, and Assembly

Generate preprocessed code (with all #include files expanded):

gcc -E test.c > test.pp

Compile to object code:

gcc test.c test2.c -o test.o

Dump the assembly:

objdump -d test.o

---

SVN and Git: Branch History, Commit Counts, Merging

Get full log history for an SVN branch using svn2git:

mkdir ORACLEPOC
cd ORACLEPOC
svn2git svn://<your-svn-server>/<repo>/UI/ORACLEPOC --rootistrunk --verbose
cd ..

Count total commits across all branches:

total=0
for i in *; do
  cd $i
  echo "In $i"
  total=`expr $total + $(git log | grep "Date:" | wc -l)`
  cd ..
done
echo $total

Merge two branches from different repositories:

git remote add MSSQL_2.3 /home/git/MSSQL_2.3
git pull MSSQL_2.3 master:b
git merge b
git branch -d b

Untrack a directory without deleting it:

git rm -r --cached <your-directory>

---

Git Tips

Undo a commit and redo it:

git reset --soft HEAD^   # undo commit, keep changes staged
# make your edits
git add .
git commit -c ORIG_HEAD  # reuse the old commit message

List all commits for a specific file:

git log -- <path/to/file>
git log --stat <path>    # shows impact of each commit

Tagging and using commit numbers as build numbers:

git tag -a v2.5 -m 'Version 2.5'
git describe --tags --long
# output: v2.5-0-deadbeef
#          ^    ^ ^
#          |    | SHA of HEAD
#          |    number of commits since last tag
#          last tag

Remove untracked empty directories:

git clean -fdn   # dry run first — shows what will be deleted
git clean -fd    # actually delete

Create a dummy/empty commit:

git commit --allow-empty -m 'Dummy commit to create the first tag'

Rename a tag (prepend a prefix):

# usage: git tag <new_tag> <old_tag> -f -m <message>
# -f forces the rename
git tag "MSSQL_2.30.0" "2.30.0" -f -m "Prepending DB type to existing tag name"

See files changed per commit (SVN -v equivalent):

git log --name-status
git log --name-only
git log --stat

---

Miscellaneous

Show timestamps in bash history:

export HISTTIMEFORMAT="%F %T "

Fix missing dependencies in CentOS:

sudo yum --disableexcludes=main install kernel-headers

Remove an invalid git remote:

git remote set-url origin git://github.com/<user>/<repo>.git