SysAdmin Tasks
A collection commands for tasks that I’ve needed to perform multiple times.
Convert PuTTY SSH2 Public Key to OpenSSH
ssh-keygen -if ssh2publickey.pub >> opensshpublickey.pub
Identify Responding Server
curl -s -I sts.psychiatrist.com|sed -n 's/^S[erv]*: //p'
Byte Order Mark (BOM)
When EZproxy configuration files are edited in Microsoft NotePad, EZproxy will complain - upon restart - about the single byte character  that begins the config.txt file. EZproxy expects UTF-8 encoding that does not start with a non-ASCII byte, like a BOM.
Using vim, does current file have a BOM?
:set bomb?
Remove BOM and write file back to disk:
:set nobomb
Print the Number of Lines in a File
Because I can never remember the command I need
wc -l <file>
Delete Old Kernels, Classic Version
uname -r # the kernel in use
dpkg -l | grep linux-image | awk '{print$2}'
apt remove --purge linux-image-3.1.0-131-generic
update-grub
Convert .mov -> .mp4 With FFMPEG
ffmpeg -i Untitled.mov -vcodec h264 -acodec mp2 Untitled.mp4
Convert .pdf -> .jpg with ImageMagick
# %d will iterate using 1 digit, %3d 3 digits
convert -density 150 art.pdf -quality 90 %d.jpg
Find the Size of a Directory
du -hs /path/to/directory
Locate all files with a specific name in the entire directory and search through those files for a line of text using regex, sort
find . -iname config.txt -exec grep "^[A-Za-z ]*\.ohionet\.org" {} \; -print | grep Name | sort
Imagemagick, Convert to Progressive JPEG
entire directory
mogrify -interlace plane *.jpg
single file
convert inputfile.jpg -interlace plane outputfile.jpg
Progressive JPEG will state, Interlace: JPEG
identify -verbose file.jpg
Globbing
# Minutes flag
-mmin +360
# Days flag
-mtime +7
# Include only files with an extension of 'txt'
find /sftp/plc/incoming/ -type f -name '*.txt' -print0
# Exclude any directories with a name that start with 'pl'. Include only files older than 30 hours.
find /sftp/[^pl]*/incoming/ -type f -mmin +1800 -print0
# Include directories with a specific name. Remove all matching files that are older than 30 hours.
find /sftp/[\(antioch\|findlay\|franciscan\|wilmington\)]*/incoming/ -type f -mmin +1800 -print0 | xargs -r0 rm --
Tuning with Sysctl
File Location on Ubuntu
nano -w /etc/sysctl.conf
Count instances of SYN received
netstat -ant|grep SYN_RECV|wc -l
Check States
netstat -nta | egrep "State|443"
netstat -nta | egrep "State|80"
Check Current Value for Parameter
sysctl -n net.ipv4.tcp_syncookies
sysctl -n net.ipv4.tcp_max_syn_backlog
sysctl -n net.ipv4.tcp_synack_retries
sysctl -n net.core.somaxconn
Reload configuration
sysctl -p
Batch Updating Files on the Server
Find files owned by a user
#find {path} -user {username}
find /usr/local -user derek
Find files assigned to a group
find {path} -group {username}
find /usr/local -group derek
Change Ownership or Group
#chown --from=olduser newuser * -R
chown --from=david derek * -R
chown --from=:1053 :derek * -R
Show Me the Redirects!
wget http://libguides.heidelberg.edu/asc 2>&1 | grep Location: