Linux Common Commands and Vi Editor Shortcuts

Oracle, PostgreSQL, MongoDB and most other databases in production run on Linux. Whatever database you manage, a big part of the day happens at the shell prompt: checking the alert log, finding what filled a disk, copying a patch between servers, or editing a parameter file in vi.

This post is the cheat sheet I wish I had when I started. The commands are grouped by task, each one has a one-line explanation, and the examples use real DBA situations. The last section is a complete vi editor reference.

Tested on: RHEL / Oracle Linux 8 and 9 with the bash shell. Almost everything works the same on other distributions. Where a command differs, the table says so.

Contents: navigation · files · viewing & searching · finding files · text processing · users & permissions · disk & memory · processes · networking · SSH · archives · system & services · vi editor

1. Navigating files and directories

Command	What it does
pwd	Print the current directory
cd /u01/app/oracle	Go to a directory
cd -	Jump back to the previous directory
cd ~	Go to your home directory
ls -l	Long listing: permissions, owner, size, time
ls -la	Include hidden files (names starting with .)
ls -lrt	Sort by time, newest at the bottom. The DBA classic for finding the latest trace or log
ls -lhS	Sort by size, largest first, human-readable
tree -L 2	Show a directory tree two levels deep (install the tree package if missing)

2. Working with files

Command	What it does
touch file.txt	Create an empty file, or update its timestamp
mkdir -p /u02/stage/patch	Create a directory, including any missing parents
cp -p fileA fileB	Copy, keeping permissions and timestamps
cp -r dirA dirB	Copy a directory recursively
mv old.log old.log.bak	Move or rename
rm file.txt	Delete a file
rm -i *.trc	Delete with a confirmation prompt for each file
rm -r dirname	Delete a directory and its contents
ln -s /u01/app/oracle/diag diag	Create a symbolic link

Careful with rm -rf. There is no recycle bin. Run ls with the same path first, and never run rm -rf with a variable that could be empty (for example rm -rf $ORACLE_HOME/ when the variable is not set).

3. Viewing and searching file contents

Command	What it does
cat file	Print the whole file
cat -n file	Print with line numbers
less file	Page through a large file. / to search, q to quit
head -50 file	First 50 lines
tail -100 alert_ORCL.log	Last 100 lines
tail -f alert_ORCL.log	Follow a file live as new lines are written (Ctrl+C to stop)
grep ORA- alert_ORCL.log	Find lines containing a string
grep -i error file	Case-insensitive search
grep -n ORA- file	Show line numbers with matches
grep -v '^#' init.ora	Hide matching lines (here: comments)
grep -c ORA-00600 file	Count matching lines
grep -rl 'LISTENER' $ORACLE_HOME/network/admin	Search recursively, list file names only
grep -B2 -A5 ORA-04031 file	Show 2 lines before and 5 after each match
wc -l file	Count lines
diff file1 file2	Show differences between two files

A real example: the 20 most frequent ORA- errors in the alert log.

grep -o 'ORA-[0-9]*' alert_ORCL.log | sort | uniq -c | sort -rn | head -20

4. Finding files

Command	What it does
find / -name sqlnet.ora 2>/dev/null	Find a file by name anywhere, hiding permission errors
find . -name '*.trc' -mtime +7	Trace files older than 7 days
find . -name '*.trc' -mtime +7 -delete	…and delete them (check without -delete first!)
find /u01 -size +1G -type f	Files larger than 1 GB
which sqlplus	Show which binary will run
locate tnsnames.ora	Fast search from a prebuilt index (run updatedb first)

5. Text processing: sort, cut, awk, sed

Command	What it does
sort file	Sort alphabetically
sort -n file	Sort numerically
sort -rn file	Numeric, largest first
sort -u file	Sort and remove duplicates
uniq -c	Count repeated adjacent lines (use after sort)
cut -d: -f1 /etc/passwd	Pick field 1 using : as the separator
awk '{print $1, $5}' file	Print columns 1 and 5
sed -n '100,200p' file	Print only lines 100 to 200
sed -i.bak 's/old/new/g' file	Replace text in place, keeping a .bak copy

6. Users, groups and permissions

Command	What it does
whoami	Current user
id oracle	User ID, primary group and all groups
sudo command	Run one command with root privileges
su - oracle	Switch to the oracle user with its full login environment
sudo useradd -m user1	Create a user with a home directory
sudo passwd user1	Set or change a password
sudo usermod -aG dba user1	Add a user to an extra group (-a append is essential, or other groups are removed)
sudo usermod -g oinstall user1	Change the user's primary group
sudo usermod -aG wheel user1	Grant sudo on RHEL / Oracle Linux (the group is sudo on Ubuntu)
sudo userdel -r user1	Delete a user and their home directory
sudo groupadd dba / groupdel dba	Create or delete a group
chmod 750 script.sh	Owner: rwx, group: r-x, others: none
chmod u+x script.sh	Make a script executable for its owner
chown -R oracle:oinstall /u01/app	Change owner and group recursively

Reading permission numbers: each digit is the sum of 4 (read) + 2 (write) + 1 (execute), for owner, group and others in that order. So 750 = rwx / r-x / ---.

Avoid chmod 777. It lets every user on the server modify the file. For scripts, 750 or 755 is almost always enough.

7. Disk and memory

Command	What it does
df -h	Free space per filesystem, human-readable
df -h /u01	Free space for one mount point
du -sh *	Size of each item in the current directory
du -sh * | sort -rh | head	The 10 largest items: find what is filling a disk
free -g	RAM and swap usage in GB
lsblk	Block devices, partitions and mount points
cat /proc/meminfo | grep -i huge	HugePages status, important for a large Oracle SGA

8. Processes and performance

Command	What it does
ps -ef | grep [p]mon	All running Oracle instances (the [p] trick hides the grep itself)
ps -ef | grep [t]nslsnr	Running listeners
ps aux --sort=-%mem | head	Top memory consumers
top	Live CPU and memory view. 1 = per-CPU, M = sort by memory, q = quit
htop	A friendlier top (install if missing)
vmstat 5 5	CPU, memory and swap every 5 seconds, 5 times
iostat -xm 5	Disk throughput and latency per device (sysstat package)
sar -u 5 5	CPU history and live samples (sysstat package)
uptime	Load average for 1, 5 and 15 minutes
kill PID	Ask a process to stop cleanly
kill -9 PID	Force-kill a process (last resort)
nohup ./job.sh > job.log 2>&1 &	Run in the background; it keeps going after you log out
jobs / fg / bg	Manage background jobs in the current shell

Never kill -9 an Oracle background process such as pmon, smon or lgwr. That crashes the instance. To end a user session, use ALTER SYSTEM KILL SESSION from SQL*Plus instead.

9. Networking

Command	What it does
ip a	Show IP addresses (replaces the older ifconfig)
ip r	Routing table (replaces netstat -r)
ss -tlnp	Listening TCP ports and which process owns them (replaces netstat -tlnp)
ss -tnp | grep 1521	Active connections to the Oracle listener port
ping -c 4 dbhost	Basic reachability test
nc -zv dbhost 1521	Check whether a port is open (telnet is often not installed)
nslookup dbhost	DNS lookup
hostname -f	Fully qualified host name
curl -O https://example.com/file.zip	Download a file over HTTP(S)
wget https://example.com/file.zip	Download a file (alternative to curl)

10. Copying between servers and SSH

Command	What it does
ssh oracle@dbhost2	Log in to a remote server
ssh-keygen -t ed25519	Create a modern SSH key pair (use -t rsa -b 4096 for older systems)
ssh-copy-id oracle@dbhost2	Install your public key for password-less login
scp file oracle@dbhost2:/u02/stage/	Copy a file to another server
rsync -avP /u02/stage/ dbhost2:/u02/stage/	Copy a directory with progress; resumes if interrupted

11. Archives and compression

Command	What it does
tar -cvf backup.tar dir/	Create a tar archive
tar -xvf backup.tar	Extract a tar archive
tar -czvf backup.tar.gz dir/	Create a gzip-compressed archive
tar -xzvf backup.tar.gz -C /target	Extract into a specific directory
tar -cjvf backup.tar.bz2 dir/	Create a bzip2 archive (smaller, slower)
tar -tvf backup.tar.gz	List the contents without extracting
gzip file / gunzip file.gz	Compress or decompress one file
unzip -q patch.zip -d /u02/stage	Extract a zip quietly into a directory

12. System information and services

Command	What it does
uname -a	Kernel version and architecture
cat /etc/os-release	Linux distribution and version
nproc	Number of CPUs
date / cal	Current date and time / a calendar
history | tail -20	The last 20 commands you ran
ulimit -a	Shell resource limits (open files, processes) for the current user
sudo systemctl status firewalld	Status of a service
sudo journalctl -xe	Recent system log messages
crontab -l / crontab -e	List or edit scheduled jobs
sudo dnf install sysstat	Install a package on RHEL 8/9 and Oracle Linux (yum on older releases, apt on Ubuntu)

13. vi / vim editor cheat sheet

vi has two main modes. In Normal mode keys are commands. In Insert mode keys type text. Press Esc at any time to return to Normal mode.

Save and quit

Keys	Action
:w	Save
:wq	Save and quit (same as ZZ)
:q	Quit (only if there are no changes)
:q!	Quit and throw away changes
:w newname	Save as a new file
:sh	Open a shell; type exit to come back to vi

Entering insert mode

Keys	Action
i	Insert before the cursor
a	Append after the cursor
A	Append at the end of the line
I	Insert at the start of the line
o	Open a new line below
O	Open a new line above

Moving around

Keys	Action
h j k l	Left, down, up, right
w b	Next word / previous word
0	Start of line
^	First non-blank character of the line
$	End of line
gg	First line of the file
G	Last line of the file
:150	Go to line 150
H M L	Top, middle, bottom of the screen
Ctrl+d Ctrl+u	Scroll half a page down / up

Editing

Keys	Action
x	Delete the character under the cursor
dw	Delete to the end of the word
D	Delete to the end of the line
dd	Delete (cut) the whole line
5dd	Delete 5 lines
dG	Delete from here to the end of the file
yy	Copy (yank) the current line
5yy	Copy 5 lines
p P	Paste after / before the cursor
S	Clear the line and start typing
u	Undo
Ctrl+r	Redo
.	Repeat the last change

Search and replace

Keys	Action
/ORA-	Search forward
?ORA-	Search backward
n N	Next / previous match
:s/old/new/	Replace the first match on the current line
:s/old/new/g	Replace all matches on the current line
:%s/old/new/g	Replace in the whole file
:%s/old/new/gc	Replace in the whole file, asking each time

Handy settings

Keys	Action
:set nu	Show line numbers (:set nonu to hide)
:set ic	Case-insensitive search
:syntax on	Syntax highlighting (vim)
:set list	Show tabs and line endings

Bonus: a quick DBA server check in one go

Paste this when you log in to an unfamiliar database server to get the big picture in a few seconds:

hostname -f; uptime; nproc; free -g
df -h | grep -v tmpfs
ps -ef | grep [p]mon
ps -ef | grep [t]nslsnr
cat /proc/meminfo | grep -i hugepages_total

Conclusion

You do not need to memorise all of these at once. Start with the ones you use daily (ls -lrt, tail -f, grep, df -h, du -sh, ps -ef) and the rest will follow. Bookmark this page and come back when you need it.

Which Linux command saves you the most time as a DBA? Share it in the comments.

Tamilselvan Perumal · Lead Product Engineer & Senior DBA