Command Reference: This content is based on the comprehensive linux-command project by jaywcjlove, licensed under the MIT License.

renice - Change process priority

The renice command alters the scheduling priority of one or more running processes. Unlike nice, which sets priority when starting a process, renice modifies the priority of already running processes.

Syntax

renice [OPTIONS] PRIORITY [[PID] ...]
renice [OPTIONS] PRIORITY -g PGID ...
renice [OPTIONS] PRIORITY -u USER ...

Common Options

-g, --pgrp: Interpret arguments as process group IDs
-p, --pid: Interpret arguments as process IDs (default)
-u, --user: Interpret arguments as usernames or user IDs
-n, --priority: Specify priority as a signed integer
-h, --help: Display help message
-v, --verbose: Verbose output
--version: Display version information

Usage Examples

Basic Usage

# Change priority of specific process
renice 10 1234

# Make process less important (higher niceness)
renice 15 5678

# Make process more important (lower niceness, requires root)
sudo renice -5 9012

Change by Process ID

# Single process
renice 5 1234

# Multiple processes
renice 10 1234 5678 9012

# Show verbose output
renice -v 15 1234

Change by User

# Change priority of all processes owned by user
renice 10 -u john

# Change priority for multiple users
renice 5 -u john mary

# Show what's being changed
renice -v 15 -u www-data

Change by Process Group

# Change priority of process group
renice 10 -g 1234

# Multiple process groups
renice 15 -g 1234 5678

Negative Niceness (Requires Root)

# Make process high priority
sudo renice -10 1234

# Make all user processes high priority
sudo renice -5 -u importantuser

Interactive Priority Adjustment

# Get PID and change priority
pid=$(pidof firefox)
renice 10 $pid

# Batch priority changes
for pid in $(pgrep firefox); do
    renice 10 $pid
done

System Administration

# Lower priority of background services
renice 15 $(pgrep backup)

# Raise priority of critical services
sudo renice -5 $(pgrep critical_service)

# Lower priority of user processes on loaded system
renice 10 -u regularuser

Priority Management

# Check current priority before changing
ps -o pid,nice,comm -p 1234
renice 5 1234
ps -o pid,nice,comm -p 1234

# Reset to default priority
renice 0 1234

Advanced Usage

# Change priority based on CPU usage
for pid in $(ps -eo pid,pcpu --sort=-pcpu | head -5 | awk '{print $1}'); do
    renice 10 $pid
done

# Lower priority of long-running processes
ps -eo pid,etime,comm | awk '$2 ~ /-/ {print $1}' | while read pid; do
    renice 15 $pid
done

Understanding the Changes

Niceness Values

Range: -20 to 19
-20: Highest priority (requires superuser)
0: Default priority
19: Lowest priority
Lower value = Higher priority
Higher value = Lower priority

Priority Inheritance

Child processes inherit parent's niceness value
Changing parent's niceness doesn't affect existing children
New children will use updated parent niceness

System Constraints

Regular users can only increase niceness (lower priority)
Only root can decrease niceness (higher priority)
Some processes may ignore renice requests

Best Practices

Use nice when starting processes instead of renice when possible
Check current priority before making changes
Use positive niceness values for background processes
Monitor effects after changing priorities

Use in scripts for dynamic priority management:

# Lower priority of CPU-intensive processes
for pid in $(pgrep -f "cpu_intensive"); do
    renice 10 $pid
done

nice: Set priority when starting processes
ps: View process priorities with ps -l
top: Monitor processes and their priorities
ionice: Set I/O scheduling priority
chrt: Change real-time attributes of processes

Troubleshooting

Common Issues

Permission denied: Need root for negative niceness values
No effect: Process may have fixed priority or ignore requests
Invalid priority: Value outside -20 to 19 range
Process not found: Check if PID is correct

Common Scenarios

# Check if change was successful
ps -o pid,nice,comm -p 1234

# Reset to default
renice 0 1234

# Change all processes of a user
renice 10 -u username

# Find PIDs of processes to change
pgrep processname | xargs renice 10

Script Examples

#!/bin/bash
# Priority management script
manage_priorities() {
    local action=$1
    local target=$2
    local priority=$3

    case $action in
        "process")
            if [ -n "$target" ] && [ -n "$priority" ]; then
                echo "Changing priority of PID $target to $priority"
                renice "$priority" "$target"
            fi
            ;;
        "user")
            if [ -n "$target" ] && [ -n "$priority" ]; then
                echo "Changing priority of user $target to $priority"
                renice "$priority" -u "$target"
            fi
            ;;
        "group")
            if [ -n "$target" ] && [ -n "$priority" ]; then
                echo "Changing priority of process group $target to $priority"
                renice "$priority" -g "$target"
            fi
            ;;
        "high-cpu")
            echo "Lowering priority of high CPU processes"
            ps -eo pid,pcpu | awk '$2 > 50 && $1 != $$ {print $1}' | while read pid; do
                renice 10 $pid
            done
            ;;
        *)
            echo "Usage: $0 {process|user|group|high-cpu} target [priority]"
            return 1
            ;;
    esac
}

# Load-based priority adjustment
adaptive_priorities() {
    local load_threshold=${1:-2.0}
    current_load=$(uptime | awk -F'load average:' '{print $2}' | awk '{print $1}' | sed 's/,//')

    if (( $(echo "$current_load > $load_threshold" | bc -l) )); then
        echo "High load detected ($current_load), adjusting priorities"
        # Lower priority of background tasks
        pgrep -f "(backup|update|index)" | while read pid; do
            renice 15 $pid
        done
    fi
}

# Service priority manager
service_priority_manager() {
    local service=$1
    local priority=$2
    local action=${3:-adjust}

    local pids=$(pgrep "$service")

    if [ -z "$pids" ]; then
        echo "No processes found for service: $service"
        return 1
    fi

    echo "Service: $service"
    echo "Action: $action"
    echo "Priority: $priority"

    case $action in
        "adjust")
            for pid in $pids; do
                renice "$priority" "$pid"
            done
            ;;
        "check")
            for pid in $pids; do
                ps -o pid,nice,pcpu,pmem,comm -p "$pid"
            done
            ;;
        "reset")
            for pid in $pids; do
                renice 0 "$pid"
            done
            ;;
    esac
}

# Usage examples
manage_priorities process 1234 10
manage_priorities user john 15
manage_priorities high-cpu
adaptive_priorities 1.5
service_priority_manager nginx 5 check
service_priority_manager nginx 10 adjust

Advanced Usage

# Intelligent priority balancer
priority_balancer() {
    local max_cpu_threshold=${1:-80}
    local target_priority=${2:-15}

    echo "Priority Balancer - $(date)"
    echo "Max CPU threshold: ${max_cpu_threshold}%"
    echo "Target priority: $target_priority"
    echo ""

    # Find processes exceeding CPU threshold
    ps -eo pid,pcpu,comm --sort=-pcpu | while read line; do
        # Skip header
        if [[ "$line" =~ ^PID ]]; then
            continue
        fi

        pid=$(echo $line | awk '{print $1}')
        cpu=$(echo $line | awk '{print $2}')
        comm=$(echo $line | awk '{print $3}')

        if [ -n "$cpu" ] && [ "${cpu%.*}" -gt $max_cpu_threshold ]; then
            echo "High CPU process: $comm (PID: $pid, CPU: ${cpu}%)"
            # Check current priority
            current_nice=$(ps -p "$pid" -o nice= | tr -d ' ')
            echo "Current niceness: $current_nice"

            if [ "$current_nice" -lt $target_priority ]; then
                echo "Raising niceness to $target_priority"
                renice "$target_priority" "$pid"
            else
                echo "Priority already acceptable"
            fi
            echo ""
        fi
    done
}

# User priority enforcement
user_priority_limits() {
    local username=$1
    local max_nice=${2:-15}

    echo "Enforcing priority limits for user: $username"
    echo "Maximum niceness: $max_nice"

    # Find all processes for user
    ps -u "$username" -o pid,nice,comm | while read line; do
        # Skip header
        if [[ "$line" =~ ^PID ]]; then
            continue
        fi

        pid=$(echo $line | awk '{print $1}')
        nice=$(echo $line | awk '{print $2}')
        comm=$(echo $line | awk '{print $3}')

        if [ "$nice" -lt $max_nice ]; then
            echo "Adjusting $comm (PID: $pid) from niceness $nice to $max_nice"
            renice "$max_nice" "$pid"
        fi
    done
}

# Time-based priority adjustment
time_based_priority() {
    local hour=$(date +%H)
    local day_of_week=$(date +%u)

    echo "Time-based priority adjustment"
    echo "Hour: $hour"
    echo "Day of week: $day_of_week"

    # Business hours: lower priority for background tasks
    if [ "$hour" -ge 9 ] && [ "$hour" -le 17 ] && [ "$day_of_week" -le 5 ]; then
        echo "Business hours - adjusting background task priorities"
        pgrep -f "(backup|update|index)" | while read pid; do
            renice 15 $pid
        done
    # Night time: higher priority for maintenance tasks
    elif [ "$hour" -ge 22 ] || [ "$hour" -le 6 ]; then
        echo "Night time - adjusting maintenance task priorities"
        pgrep -f "(backup|cleanup|maintenance)" | while read pid; do
            renice 5 $pid
        done
    fi
}

# Batch job priority manager
batch_job_manager() {
    local action=$1
    local job_pattern=$2
    local priority=${3:-10}

    case $action in
        "lower")
            echo "Lowering priority of jobs matching: $job_pattern"
            pgrep -f "$job_pattern" | while read pid; do
                renice "$priority" "$pid"
            done
            ;;
        "raise")
            echo "Raising priority of jobs matching: $job_pattern"
            pgrep -f "$job_pattern" | while read pid; do
                renice "$priority" "$pid"
            done
            ;;
        "status")
            echo "Status of jobs matching: $job_pattern"
            pgrep -f "$job_pattern" | while read pid; do
                ps -o pid,nice,pcpu,pmem,etime,comm -p "$pid"
            done
            ;;
        *)
            echo "Usage: $0 {lower|raise|status} pattern [priority]"
            ;;
    esac
}

# Usage examples
priority_balancer 75 12
user_priority_limits regularuser 12
time_based_priority
batch_job_manager lower ".*backup.*" 15
batch_job_manager status ".*backup.*"

Monitoring and Maintenance

# Priority monitoring script
monitor_priorities() {
    local interval=${1:-30}
    local log_file=${2:-"/tmp/priority_monitor.log"}

    while true; do
        echo "$(date): Priority Monitor Check" >> "$log_file"
        echo "System Load: $(uptime)" >> "$log_file"

        # Check processes with unusual priorities
        ps -eo pid,nice,comm | awk '$2 < 0 || $2 > 10 {print $1, $2, $3}' >> "$log_file"

        # Check high CPU processes
        ps -eo pid,nice,pcpu,comm --sort=-pcpu | head -5 >> "$log_file"
        echo "--------------------------------" >> "$log_file"

        sleep $interval
    done
}

# Automatic priority adjustment based on system load
auto_priority_adjust() {
    local load_threshold_low=${1:-1.0}
    local load_threshold_high=${2:-3.0}
    local low_priority=${3:-15}
    normal_priority=5

    current_load=$(uptime | awk -F'load average:' '{print $2}' | awk '{print $1}' | sed 's/,//')

    echo "Current load: $current_load"

    if (( $(echo "$current_load > $load_threshold_high" | bc -l) )); then
        echo "High load detected, lowering priority of background tasks"
        pgrep -f "(backup|update)" | while read pid; do
            renice $low_priority $pid
        done
    elif (( $(echo "$current_load < $load_threshold_low" | bc -l) )); then
        echo "Low load detected, normalizing priority of background tasks"
        pgrep -f "(backup|update)" | while read pid; do
            renice $normal_priority $pid
        done
    else
        echo "Load is normal, no priority adjustment needed"
    fi
}

# Process cleanup with priority adjustment
cleanup_with_priority() {
    local process_pattern=$1
    local max_age=${2:-3600}  # 1 hour
    local final_priority=${3:-19}

    echo "Cleaning up processes matching: $process_pattern"
    echo "Max age: $max_age seconds"
    echo "Final priority: $final_priority"

    # Find old processes and raise their niceness
    ps -eo pid,etime,comm | grep -E "$process_pattern" | while read line; do
        pid=$(echo $line | awk '{print $1}')
        age_str=$(echo $line | awk '{print $2}')
        comm=$(echo $line | awk '{for(i=3;i<=NF;i++) printf "%s ", $i; print ""}')

        # Parse age
        if [[ "$age_str" =~ ([0-9]+)-([0-9]{2}):([0-9]{2}):([0-9]{2}) ]]; then
            days=${BASH_REMATCH[1]}
            hours=${BASH_REMATCH[2]}
            age_seconds=$((days * 86400 + hours * 3600))

            if [ $age_seconds -gt $max_age ]; then
                echo "Old process found: $comm (PID: $pid, age: $age_str)"
                renice $final_priority $pid
                echo "Priority set to $final_priority, process will be terminated if it continues"
            fi
        fi
    done
}

# Usage
monitor_priorities 60
auto_priority_adjust 1.5 3.0 15
cleanup_with_priority "old_process.*" 7200 18

Syntax​

Common Options​

Usage Examples​

Basic Usage​

Change by Process ID​

Change by User​

Change by Process Group​

Negative Niceness (Requires Root)​

Interactive Priority Adjustment​

System Administration​

Priority Management​

Advanced Usage​

Understanding the Changes​

Niceness Values​

Priority Inheritance​

System Constraints​

Best Practices​

Related Commands​

Troubleshooting​

Common Issues​

Common Scenarios​

Script Examples​

Advanced Usage​

Monitoring and Maintenance​

Syntax

Common Options

Usage Examples

Basic Usage

Change by Process ID

Change by User

Change by Process Group

Negative Niceness (Requires Root)

Interactive Priority Adjustment

System Administration

Priority Management

Advanced Usage

Understanding the Changes

Niceness Values

Priority Inheritance

System Constraints

Best Practices

Related Commands

Troubleshooting

Common Issues

Common Scenarios

Script Examples

Advanced Usage

Monitoring and Maintenance