Optimisation des performances

# Install (usually pre-installed on Ubuntu 26.04)
sudo apt install htop
 
# Launch
htop

# top - basic process monitoring
top
 
# vmstat - virtual memory statistics
vmstat 1 5    # once per second, 5 times
 
# iostat - I/O statistics
sudo apt install sysstat
iostat -xz 1
 
# iotop - view per-process I/O
sudo apt install iotop
sudo iotop
 
# nmon - comprehensive performance monitoring
sudo apt install nmon
nmon
 
# glances - modern system monitoring
sudo apt install glances
glances
 
# btop - visually appealing resource monitor
sudo apt install btop
btop

# CPU information
lscpu
cat /proc/cpuinfo | grep "model name" | head -1
 
# Memory information
free -h
cat /proc/meminfo
 
# Disk usage
df -h
 
# Load averages
uptime
cat /proc/loadavg
 
# Network connections
ss -tunapl

# cpufrequtils is deprecated; use cpupower instead (provided by linux-tools)
sudo apt install linux-tools-common linux-tools-generic
 
# View current CPU frequency and governor
cpupower frequency-info
 
# View available frequency governors
cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors
 
# Set to performance mode
sudo cpupower frequency-set -g performance
 
# Set to power-saving mode
sudo cpupower frequency-set -g powersave

# List available power profiles
powerprofilesctl list
 
# Switch to performance mode
powerprofilesctl set performance

# Use nice to start a process (-20 to 19, lower values = higher priority)
nice -n 10 /path/to/task.sh
 
# Change the priority of a running process
renice -n 5 -p PID
 
# Set real-time priority
sudo chrt -f 50 /path/to/realtime-task
 
# Pin a process to specific CPU cores
taskset -c 0,1 /path/to/task.sh

# View current swap usage
swapon --show
free -h
 
# View current swappiness value (default is 60)
cat /proc/sys/vm/swappiness

# Temporarily change swappiness
sudo sysctl vm.swappiness=10
 
# Permanently change swappiness
echo "vm.swappiness=10" | sudo tee -a /etc/sysctl.d/99-performance.conf
sudo sysctl --system

# Cache pressure (default 100; lower values retain more directory and inode caches)
echo "vm.vfs_cache_pressure=50" | sudo tee -a /etc/sysctl.d/99-performance.conf
 
# Dirty page writeback policy
echo "vm.dirty_ratio=15" | sudo tee -a /etc/sysctl.d/99-performance.conf
echo "vm.dirty_background_ratio=5" | sudo tee -a /etc/sysctl.d/99-performance.conf
 
# Apply all changes
sudo sysctl --system

# Free page cache
sudo sync; echo 1 | sudo tee /proc/sys/vm/drop_caches
 
# Free dentry and inode cache
sudo sync; echo 2 | sudo tee /proc/sys/vm/drop_caches
 
# Free all caches
sudo sync; echo 3 | sudo tee /proc/sys/vm/drop_caches

# View current I/O scheduler
cat /sys/block/sda/queue/scheduler
# Example output: [mq-deadline] kyber bfq none
 
# Temporarily change
echo "bfq" | sudo tee /sys/block/sda/queue/scheduler

sudo nano /etc/udev/rules.d/60-scheduler.rules

# HDD uses mq-deadline
ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/rotational}=="1", ATTR{queue/scheduler}="mq-deadline"

# SSD uses none or mq-deadline
ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/rotational}=="0", ATTR{queue/scheduler}="mq-deadline"

# NVMe uses none
ACTION=="add|change", KERNEL=="nvme[0-9]*", ATTR{queue/scheduler}="none"

sudo udevadm control --reload-rules

# Check if the SSD supports TRIM
sudo hdparm -I /dev/sda | grep TRIM
 
# Manually run TRIM
sudo fstrim -v /
 
# Check the scheduled TRIM service
systemctl status fstrim.timer
 
# Enable scheduled TRIM (runs weekly)
sudo systemctl enable --now fstrim.timer

# Recommended SSD mount options
UUID=xxxx  /  ext4  defaults,noatime,discard  0  1

# Mount /tmp to memory
# Add to /etc/fstab:
# tmpfs  /tmp  tmpfs  defaults,noatime,size=2G  0  0
 
# Reduce journal writes
sudo nano /etc/systemd/journald.conf
# Set: Storage=volatile   (memory only, lost after reboot)
# Or: SystemMaxUse=100M   (limit journal size)

sudo nano /etc/sysctl.d/99-network.conf

# TCP buffer sizes
net.core.rmem_max=16777216
net.core.wmem_max=16777216
net.ipv4.tcp_rmem=4096 87380 16777216
net.ipv4.tcp_wmem=4096 65536 16777216

# TCP connection optimization
net.ipv4.tcp_fastopen=3
net.ipv4.tcp_mtu_probing=1
net.ipv4.tcp_congestion_control=bbr

# Connection queue
net.core.somaxconn=65535
net.core.netdev_max_backlog=65535

# TIME_WAIT optimization
net.ipv4.tcp_tw_reuse=1
net.ipv4.tcp_fin_timeout=15

# Enable BBR congestion control
echo "net.core.default_qdisc=fq" | sudo tee -a /etc/sysctl.d/99-network.conf
echo "net.ipv4.tcp_congestion_control=bbr" | sudo tee -a /etc/sysctl.d/99-network.conf
sudo sysctl --system
 
# Verify BBR is active
sysctl net.ipv4.tcp_congestion_control

# View filesystem parameters
sudo tune2fs -l /dev/sda2
 
# Reduce reserved space (default 5%, can be lowered for large partitions)
sudo tune2fs -m 1 /dev/sda2

# View current limit
ulimit -n
 
# Temporarily increase the limit
ulimit -n 65535
 
# Permanently change
sudo nano /etc/security/limits.conf

# /etc/security/limits.conf
*  soft  nofile  65535
*  hard  nofile  65535

echo "fs.file-max=2097152" | sudo tee -a /etc/sysctl.d/99-performance.conf
sudo sysctl --system

# Analyze boot time
systemd-analyze
 
# View boot time per service
systemd-analyze blame
 
# View critical boot path
systemd-analyze critical-chain
 
# Disable unnecessary services
sudo systemctl disable bluetooth.service     # not using Bluetooth
sudo systemctl disable cups.service          # not using printing
sudo systemctl disable ModemManager.service  # not using modem
 
# Check boot log for errors
journalctl -b -p err

# Disk performance test
sudo apt install fio
 
# Sequential read test
fio --name=seqread --rw=read --bs=1M --size=1G --numjobs=1 --runtime=30
 
# Random read/write test
fio --name=randreadwrite --rw=randrw --bs=4k --size=1G --numjobs=4 --runtime=30
 
# Simple disk write speed test
dd if=/dev/zero of=/tmp/testfile bs=1M count=1024 oflag=direct
 
# Memory bandwidth test
sudo apt install sysbench
sysbench memory run
 
# CPU benchmark
sysbench cpu --threads=$(nproc) run
 
# Network performance test
sudo apt install iperf3
# Server: iperf3 -s
# Client: iperf3 -c server_ip