Question

Alright,
I’m thinking of creating a webscript that depends on cronjob..
I’m wondering, would it ever make any server damages for the amount of crontabs ?

lets say i have 50 crontabs to be done everyday, would it ever hurt the server ?
if no, what’s the max amount of crontabs to be added in a linux server @ 512MB memory

Answer 1

When you create a new job the cron daemon call the function job_add (job.c), this function alloc the memory to the job and add it to the tail of the job list.
The job is allocated on the heap, so theorically you’re limited just by the RAM installed on your machine.

Some notes from the CRON code:

The job structure:

typedef struct _job {
    struct _job     *next;
    entry           *e;
    user            *u;
} job;

Each user crontab entry is defined by:

typedef struct _entry {
        struct _entry   *next;
        uid_t           uid;
        gid_t           gid;
        char            **envp;
        char            *cmd;
        bitstr_t        bit_decl(minute, MINUTE_COUNT);
        bitstr_t        bit_decl(hour,   HOUR_COUNT);
        bitstr_t        bit_decl(dom,    DOM_COUNT);
        bitstr_t        bit_decl(month,  MONTH_COUNT);
        bitstr_t        bit_decl(dow,    DOW_COUNT);
        int             flags;
#define DOM_STAR        0x01
#define DOW_STAR        0x02
#define WHEN_REBOOT     0x04
} entry;

And the user struct:

typedef struct _user {
        struct _user    *next, *prev;   /* links */
        char            *name;
        time_t          mtime;          /* last modtime of crontab */
        entry           *crontab;       /* this person's crontab */
} user;

You can see that this structs does not cosume a lot of memory.
If you’re curious about how the implementation of cron work, you can see the code here : cron ubuntu source.