asp.net中ashx生成验证码代码放在Linux(centos)主机上访问时无法显示问题

Application Exception
System.ArgumentException
The requested FontFamily could not be found [GDI+ status: FontFamilyNotFound]

Description: HTTP 500.Error processing request.
Details: Non-web exception. Exception origin (name of application or object): System.Drawing.
Exception stack trace:
  at System.Drawing.GDIPlus.CheckStatus (Status status) [0x00000] in <filename unknown>:0 
  at System.Drawing.FontFamily..ctor (GenericFontFamilies genericFamily) [0x00000] in <filename unknown>:0 
  at (wrapper remoting-invoke-with-check) System.Drawing.FontFamily:.ctor (System.Drawing.Text.GenericFontFamilies)
  at System.Drawing.FontFamily.get_GenericMonospace () [0x00000] in <filename unknown>:0 
  at EnterpriseShow.UI.Manager.AjaxHandle.ValidCode.ProcessRequest (System.Web.HttpContext context) [0x00000] in <filename unknown>:0 
  at System.Web.HttpApplication+<Pipeline>c__Iterator1.MoveNext () [0x00000] in <filename unknown>:0 
  at System.Web.HttpApplication.Tick () [0x00000] in <filename unknown>:0 

context.Response.ContentType = "image/gif";
            Bitmap basemap = new Bitmap(200, 60);
            Graphics garph1 = Graphics.FromImage(basemap);

            garph1.FillRectangle(new SolidBrush(Color.White), 0, 0, 200, 60);
            Font font = new Font("consola.ttf", 48, FontStyle.Bold, GraphicsUnit.Pixel);

            Random r = new Random();
            string letters = "ABCDEFGHIJKLMNPQRSTUVWXYZ";
            string letter;
            StringBuilder s = new StringBuilder();
            for (int i = 0; i < 5; i++)
            {
                letter = letters.Substring(r.Next(0, letters.Length - 1), 1);
                s.Append(letter);
                garph1.DrawString(letter, font, new SolidBrush(Color.Black), i * 38, r.Next(0, 15));

            }

            Pen linePen = new Pen(new SolidBrush(Color.Black), 2);
            for (int x = 0; x < 6; x++)
            {
                garph1.DrawLine(linePen, new Point(r.Next(0, 199), r.Next(0, 59)), new Point(r.Next(0, 199), r.Next(0, 59)));
            }

            basemap.Save(context.Response.OutputStream, ImageFormat.Gif);
            context.Session["CheckCode"] = s.ToString();    //存入Session，用于对比验证
            context.Response.End();